#geometry-and-trigonometry

1 messages · Page 191 of 1

sick veldt
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what?

upper karma
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If you have to ask here to verify the answer, you don't understand it @upper karma so stop

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Ask only if you get the wrong answer and don't understand why

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you should verify it yourself and make sure it's right on your own

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not guess then ask here if it's right

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im only 12

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im trying to learn geometry

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none of this is for my benefit

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if it's not for your benefit then don't learn it lmao

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it is for my benefit

sick veldt
upper karma
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i just don't gain anything but knowledge

sick veldt
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Is this proof correct?

upper karma
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you just said it wasn't

sick veldt
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I believe the last box should be HL

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but I'm not so sure

upper karma
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you highly underestimate the value of knowledge lmao

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…..?

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good luck being a redneck who don't know whether the earth is flat or nah

sick veldt
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what are you talking about

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lol

upper karma
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wow..

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he's being rude to me because im asking help

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you didn't ask for help lmfao

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you just asked someone to verify your blind guess

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it wasn't a blind guess

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then answer me, why would that answer not be right?

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ive been stuck on the same problem for 35 minutes

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because their not congruent

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but that makes no sense because length wise, they look like they are

sick veldt
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whats not congruent

upper karma
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SNK AND RNL

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length is irrelevant

sick veldt
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yeah...

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the angles look corresponding

upper karma
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that's what i meant

sick veldt
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parallel lines that is

upper karma
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the angles look congruent/corresponding

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just inverted

sick veldt
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idk dude haha

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I just need to know if my answers are correct

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next time

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Explain what you did like I did

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after sending a question

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<@&286206848099549185>

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help pls

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I need help with this

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15 min already

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Number one might be a rectangle

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and the last box might be SAS

tacit sparrow
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Yeah that’s not the definition of a parallelogram

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Parallelograms don’t have right angles

sick veldt
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right

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And for the last one?

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it would be HL

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cause it does have a rectangle

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with right angles

tacit sparrow
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Yeah that’s HL I think

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HL is just specialized SAS anyway

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Where the angle is right

sick veldt
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@tacit sparrow Sorry to bother you again, but could you also confirm this one?

tacit sparrow
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Looks fine to me
I don’t rly remember all of the terms from geometry but

upper karma
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how do I go abouts solving this

tacit sparrow
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Well BC and DE being parallel would make ABC and ADE similar

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How would you contradict that

sick veldt
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Looks like the second option

tacit sparrow
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Yeah

sick veldt
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remember

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always add the ratios

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you're gonna use that later on

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with partitions

merry siren
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How do i get AE

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BE is 20.8

upper karma
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?help

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!help

merry siren
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!help

sick veldt
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<@&286206848099549185> Three people here need assistance

upper karma
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yeah i’m kinda busy now doing work too

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Lol

jaunty horizon
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Perhaps you should use a fraction

merry siren
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Do it sir

dire rampart
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oof

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@sick veldt thats correct

sick veldt
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thanks

spring apex
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@sick veldt still need help?

sick veldt
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yeah

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i got another one

spring apex
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If a line is perpendicular to another line

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What does this mean?

sick veldt
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No I answered that already

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This one I'm working

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on

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I haven't graphed it yet

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but heres what I have written down so far

spring apex
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Oh you pinged helpers for someone else’s question

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Big mistake

sick veldt
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No lol

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I pinged for mines

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and the other guy

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i included myself

spring apex
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Well idk about that graph thing so 🤷

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But I can tell you about the perpendicular line

sick veldt
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sigh

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FINALLY

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done

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Is this graphed correctly?

upper moat
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The point at (4, 3) should be at (4, 4), since we’re doubling the distance from (-2, -2) to (1, 1)

tawdry cape
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guys, if i want to find the x intercepts of 2sinx + 1 = 0, the first one is -1/2 and second is 7pi/6. but how is the second one found?

somber coyoteBOT
serene field
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The sine inverse function yields the quadrant 1 or quadrant 4 solution.

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In order to find the other solution, we take a look at the unit circle.

bitter stratus
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what is the derivative of

gritty siren
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=pup derivative sin^2(x)-2cos^2(x)

charred spearBOT
hard gale
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proof by wa

serene field
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🤔

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I'm getting a different solution

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Wait, it's the same thing.

gritty siren
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It's got a nice expression surprisingly

bitter stratus
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i dont get it though

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how does it become that

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this is how i did it ;-;

hard gale
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🤕 my chain rule hurts......

upper karma
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My calc 2 professor made this one of our standard derivatives actually

hard gale
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so you can write $\sin^2$ as $sq\circ\sin$, with $sq : x \mapsto x^2 \$ therefore $\left(sq \circ\sin\right)^{'} = \sin^{'} * (sq^{'} \circ \sin)$, ie $$ \boxed{\left(\sin^2\right)' = 2\sin\cos}$$

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almost the same thing for cos^2

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wat

upper karma
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The fuck did you do lol

hard gale
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fack tex

somber coyoteBOT
bitter stratus
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is this an identity?

hard gale
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if you want

bitter stratus
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what

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im lost

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product rule?

hard gale
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chain rule demit

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i've said it at the beginning

bitter stratus
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wait

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oh

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it makes sense

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thank you

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sorry

upper karma
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“Demit”

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I’m stealing dis

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K bye

hard gale
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so concise lel

steady sleet
queen socket
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So if the slope of a line is the tangent does that mean the hyptonese of a triangle is equal to the tangent?

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Because tan = a^2+b^2= c^2 or sin/cos =tan

spring apex
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The slope of a line is it’s gradient

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Is it’s rate of change

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I’m not sure exactly what you mean by the slope of a line is the tangent

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If you put it into context

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Suppose I have a car which drives at 3m/s east and 4m/s north

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Then the car is driving 5m/s at an angle of x = tan^-1(4/3)

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But yeah could you elaborate more on your question?

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@queen socket

queen socket
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Like in a unit circle your hypo is equal to one and your x = cos and y = sin and using the trig identity x2 +y2 =1^2

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So your hypo is also the length of the radius of the unit circle

spring apex
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For me I would say you are overthinking it a bit, the tangent to something is the straight line or plane which touches a curved line or surface at one and only one point

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To call the hypotenuse of a triangle the ‘tangent’ is a bit strange to me

queen socket
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Oh okay

spring apex
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But I would also ask someone else because I could be completely off

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sorry I couldn’t give you the answer you may have been looking for

queen socket
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I just looked it up, it says the following in calculus, the slope of a function at a given point is the slope of the tangent line. However, not every line with the same slope is tangent.

spring apex
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No I know what a tangent is with calculus

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I meant I could be off about the trig stuff

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Is the tangent the hypotenuse, maybe 🤷 I’ve never heard of it personally

queen socket
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Thats all good, have you been unbanned from piano yet

spring apex
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Lol nope

queen socket
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Unlucky

woeful flame
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why my answer is incorrect?

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:\

boreal warren
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derivative of 2/(x^2+2x) is wrong

woeful flame
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why?

boreal warren
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try using the full quotient rule instead of the chain rule

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d/dx (u/v) = (u'v-v'u)/v^2

woeful flame
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😮

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sorry but i didnt understand

boreal warren
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idk how to use the LaTeX bots so can't write it out clearer 😄

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do u know the quotient rule? or have u used it before?

woeful flame
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i did:
(2')(x^2+2x) - (-2)((x^2+2x) ') / (x^2+2x)^2

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that should be ok

boreal warren
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seems correct

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now simplify

woeful flame
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I got -4x-4 / (x^2+2x)^2

boreal warren
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o.O how?

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2' = 0 so the first term is gone completely

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(x^2+2x)' = 2x+2

woeful flame
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Fixed

boreal warren
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ah yes

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thats correct 😄

woeful flame
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but that what I sent

boreal warren
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oh yea

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well derivative calculators are giving me the answer in a different form

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they factorise the denominator into x^2 (x+2)^2

woeful flame
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i dont understand

boreal warren
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sorry u were correct all along haha

woeful flame
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my english is very bad

boreal warren
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i think

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hmm i can't think why it is marked wrong#

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try just expanding the denominator into the form x^2*(x+2)^2, even though it should be equivalent the computer may only recognise it in a particular form depending on how the question is coded

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i worked for my uni's maths department writing online quiz questions... sometimes it can be difficult to code such things to recognise all inputs

spring apex
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=pup derive \frac{1}{x+2} + \frac{2}{x^{2}+2x} - \frac{1}{x} + 3

charred spearBOT
spring apex
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=pup derivative \frac{1}{x+2} + \frac{2}{x^{2}+2x} - \frac{1}{x} + 3

charred spearBOT
spring apex
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?!

boreal warren
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well i didn't anticipate that

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if its a half decent program it should recognise that it simplifies to zero on its own

spring apex
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=pup derive \frac{1}{x+2}

charred spearBOT
spring apex
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=pup derive \frac{2}{x^{2}+2x}

charred spearBOT
spring apex
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There’s where you went wrong

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Did you write that?

boreal warren
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ye he got that

spring apex
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He did?

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I thought it was something different

boreal warren
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denominator was written differently

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in the form (x^2+2x)^2

spring apex
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Try writing the minus out of the fraction

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So instead of -1/2

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It’s -(1/2)

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I know it’s the same but computer tests are retarded

boreal warren
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they are... very xD

glacial hazel
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Hello

steady sleet
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no

elfin mica
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is there a formula for sinθcosθ again?

warm pine
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Split it in to 12 triangles

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sinxcosx = (1/2)sin2x

elfin mica
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ok thanks

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im rechecking my work then ill ask for help again

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ahh ok i found my mistake

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thanks for the assistance btw

valid pike
serene field
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Make a triangle with x as the hypotenuse

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Relate the side lengths of the outer and inner triangles

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Pythagorean Theorem to solve for x

valid pike
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Thanks

elfin moon
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Not sure where this goes but what is this problem called?

Given a polygon P with holes (obstacles inside P) and a point q, find q' that is furthest away from q (Euclidian distance) and not on a boundary of P

upper karma
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what are the conditios for 2 segments to intersect?

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defined each segment with 2 points

keen aspen
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The slopes have to be different

upper karma
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something else?

kind mist
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Stuck on #9 pls help

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Ive got the solutions pi/6 and pi/3 but not the other two

keen aspen
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There are 2 solutions in (0, 2pi]

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Look on the unit circle to see where sine is positive and has the same reference angle

upper karma
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I Need help

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#smart peaple plz help meh

chrome fiber
upper karma
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Lead has a density of 11.35g/cm"3. Calculate the maximum number of lead spheres of radius 1.5mm that can be made from 1kg of gold

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@chrome fiber if you can help be that would be awesome!

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😦

upper karma
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guys help

plucky marlin
upper karma
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we have three points: A(-1,3), B(1,4), C(3,y)

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they are collinear

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we wanna find y

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how can i do that ?

plucky marlin
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the line connecting those points would have the same slope

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or u could connect those points and say that the area = 0

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and then solve for y

upper karma
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let me try that first one then i'll come back with the results

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ok solved thanks

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y = 5

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hi can i also post a question here? or does it have to be in the questions channel

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it's about analytical geometry

hard gale
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you can post it here

upper karma
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thank you 😃

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Q: if the line segment connecting (x, 3) and (5, y) is bisected by the point (7, -5) , find the value of x and y

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i tried to come up with equations however still haven't found the answer

hard gale
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bisected, ie the point in the middle of the line segment is (7, -5)? (my geo vocab in english is pretty bad)

upper karma
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bisected means it divides the line in two specifically at the middle

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oh wait hahaha

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i think i get it now lol

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i was thinking point 7,-5 is not the one in the middle

hard gale
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oof

upper karma
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omg you're a genius octo!!! thank you!!!!

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i can solve this now

hard gale
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👌

upper karma
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Lead has a density of 11.35g/cm"3. Calculate the maximum number of lead spheres of radius 1.5mm that can be made from 1kg of gold

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pls help meh

hard gale
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"Calculate the maximum number of lead spheres of radius 1.5mm that can be made from 1kg of gold" dafuq?

crisp hornet
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Density*volume=mass

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Convert the g/cm”3 to kg/m”3

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And find the volume of each lead sphere(4/3 * pi*r^3)

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Multiply both to get mass of one lead sphere

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Then equate the masses to find the no. Of spheres required

civic monolith
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can someone help me?

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i’m doing geometry

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kinda understand nothing

dire rampart
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sure, ask your question

civic monolith
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so this question says “(3,-7) and 3x-4y=12 write an equation for a line perpendicular”

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i literally know nothing of what i’m doing

serene field
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What is the slope of a line that is perpendicular to another?

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More specifically, what slope will be perpendicular to the given linear equation?

upper karma
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the relation is given by (slope1)*(slope2) = -1

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lets say the slope of a line is 5, then the slope of a line perp to it is -1/5

upper karma
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Lead has a density of 11.35g/cm"3. Calculate the maximum number of lead spheres of radius 1.5mm that can be made from 1kg of gold

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plz help

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bk thx but i dont think that worked

keen tangle
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how do you even make lead spheres of gold?

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reverse philosopher's stone

dire rampart
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atom bender

civic monolith
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sorry i never responded back, but i understand my question now so thanks

upper karma
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i need halp plz

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XD

trail helm
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I need help with factoring

sly belfry
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@trail helm go ahead

frozen saffron
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Hellp

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I need help

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So I have 10th grade math right now and I need some help about similar triangles.

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Like SOH CAH TOA

trail helm
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IM in 8th grade geometrey rn and my teacher is useless

frozen saffron
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maybe I can help you

trail helm
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I need help with factoring

frozen saffron
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what kind of factoring?

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binomials?

trail helm
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10x^2 + 27x + 5

frozen saffron
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so basically u need to transform that on a factored from

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gimme a minute

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imma solve it for you

trail helm
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I just need help cuz I have a semester test tmmrw

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And im doing the study guide

frozen saffron
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do you know the criss cross method?

trail helm
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No

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I knno the greatest common factor thingy

frozen saffron
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do that to find the factored form of that equation

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imma show the procedures to you aight

trail helm
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2x^2 + 27x + x

frozen saffron
trail helm
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What about the exponent

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Ill try that

frozen saffron
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the exponent will be gone

trail helm
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Ok

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How would I use that on 10x^2 + 27x + 5

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Im confused

frozen saffron
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multiply any number that can result to 10

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like 5 x 2

trail helm
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Oh ok

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How about the 5

somber coyoteBOT
serene field
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We can then factor by grouping.

frozen saffron
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that procedure is way too confusing

serene field
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Product of the first and last

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Add up to the middle

trail helm
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@frozen saffron Thank you

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That makes sense now

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I got (5x+1)(2x+5)

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I think thats right, right?

frozen saffron
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yup

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remember always check the middle

trail helm
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Ok

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What do you mean

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How do I check the middle

frozen saffron
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I mean you need to have the same result like in the middle

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if you cross multiply

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So can someone help me about my similar triangles thing?

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I need a help about SOH CAH TOA

upper karma
frozen saffron
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80 i think

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because the other line is parallel to that one

serene field
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Just ask, Chris

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Many of us know enough trig to help out. 🤔

frozen saffron
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Can someone help me out?

serene field
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,rotate 90

somber coyoteBOT
serene field
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Draw out your diagram

frozen saffron
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kk

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Is that correct?

serene field
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Looks right.

frozen saffron
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how do I find the height tho?

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the total height

burnt relic
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im a grade 10 but ill try to help

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add up the angles on the left 37 and 58

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or whatever they were

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then use tan(angle on left)=x/9.8

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tan because the angle in question is adj and u are trying to find the opp so tan uses that

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to solve just do tan of the angle then multiply by 9.8(cross multiply)

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^^^^

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not sure if correct but pretty sure

woven wigeon
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yeah its fine

serene field
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It only implies the angle of elevation from the anchor point to the top of the tower is 58 degrees from the base, not 58 degrees on top of the 37 degree angle

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If it were 58 degrees on the 37, that would be > 90 and there would be an obtuse angle.

woven wigeon
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owo, so its not a right triangle 🤔

burnt relic
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oh ur right

serene field
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We have a triangle with two known angles and one side. We can easily find the third angle by the sum of angles of a triangle. Law of sines should quickly find the solution.

burnt relic
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lol rip sry

woven wigeon
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damn big f

serene field
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This question threw me off too. 🤔

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Don't really need the 37 degree thing, as far as I can see it.

burnt relic
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Anyways, can i get some help on this?

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Maria needs to load cars onto a transport
truck. She is planning to drive up a ramp, onto the truck bed. The truck bed is 1.5 m high, and the maximum angle of the slope of the ramp is 35 degrees .

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How long should the ramp be? Round your
answer to one decimal place.

serene field
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Draw your diagram

woven wigeon
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so basically sin(35)=1.5/x.... hopefully lo im not a math person

serene field
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You know you have a right triangle and can find all angles via sum of angles. Law of sines looks like it'd work here as well.

burnt relic
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ya i was just gonna ask about that

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idk about that studd yet

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stuff

woven wigeon
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same

serene field
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Then work with SOHCAHTOA

burnt relic
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we have a test on cos,tan,sin and sim triangles

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tom

serene field
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Have you created your diagram?

burnt relic
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i ahve but cant send a pic

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but angle on left is 35

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and height (or opp to angle) is 1.5

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m

serene field
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You have multiple ways to go about this, but your goal is basically to find the length of the ramp.

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Tbh, based on the question, I'm not sure whether they want the second leg or the hypotenuse. GWcfcThonk

woven wigeon
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the hypo

burnt relic
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thats what i thought

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but i did both

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and did not get either of them to what the ans was

serene field
#

Well then, look at your trigonometric ratios.

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Only sine and cosine have hypotenuse, so those will get us to the hypotenuse.

woven wigeon
#

owo

serene field
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With respect to the 35 degree angle, for example, we would need to use sine.

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As we don't have the length of the adjacent.

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With respect to the 55 degree angle, cosine would be needed, as we don't have the length of the opposite to that angle.

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Either way, you can solve for hypotenuse.

burnt relic
#

okay thanks for that. I will try it out

summer barn
merry bough
#

@summer barn what formulas do you have that relate cosine and sine?

summer barn
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cos^2x+sin^2x=1

merry bough
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what else?

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something that has adding in the brackets like cos(x+b) = sin??

burnt relic
#

Peggy’s Cove Lighthouse in Nova Scotia is possibly the most photographed lighthouse in the world. The observation deck is about 20 m above sea level. From the observation deck, the angle of depression to a boat is 6°. How far from the boat is the lighthouse, to the nearest metre?

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^^^^^^^^^^^

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can i get some help w/ that please

mystic shadow
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did you try a picture?

burnt relic
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sry for bad quality but top right is 6

timber hinge
#

They cram so much useless shit into those questions

burnt relic
#

left*

mystic shadow
#

okay which side is the side youre trying tosolve for

burnt relic
#

opposite to the angle right?

timber hinge
#

Hypotenuse

mystic shadow
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pretty sure they mean the bottom side

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that is the distance from the lighthouse to the boat

burnt relic
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k so if i were to find the bottom side,

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i would do tan 6=x/20

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but that leaves me with 2.1

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which is not the answer

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and i fi were to solve for hypotenuse,

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i would do cos 6 = 20/x

mystic shadow
#

it asks for the nearest metre

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try inputting 2 m

burnt relic
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ohh i think i got it

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my problem was with doing the tan not rounding

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but thanks for your help!

mystic shadow
#

np

burnt relic
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I actually need a bit more help lol

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If you were in a hot air balloon at a vertical height of 500 m above the ground, at what angle of depression would you look at a point on the ground 800 m horizontally on the ground from directly under the balloon?

mystic shadow
#

you need to use an inverse trig function on your calculator

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otherwise it's solved the same as the last problem

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try drawing the picture first

glad ocean
#

is it arctan (800/500)?

mystic shadow
#

seems right

upper karma
#

Boi

mystic shadow
#

@upper karma ?

upper karma
#

whats up?

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Is it fine that I forget triggernometry cuz I moved on xD

summer barn
#

@merry bough cos(x+3/2π) right?

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sorry i was away just now

upper karma
#

@glad ocean yesh that should be rigth

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right

glad ocean
#

one does not simply move on from trigonometry

serene field
#

I mean, I haven't done trig stuff since calc 3-ish GWcfcThonk

burnt relic
#

its pretty easy im just not understanding it rn

summer barn
#

@burnt relic find CB using pythag

burnt relic
#

ive done that

summer barn
#

find the scale factor

upper karma
#

^

serene field
#

I would find angle BAC and use tangent, but that works too 👀

upper karma
#

Then you get DA

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Then you minus BA

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I guess

summer barn
#

^

timber hinge
#

rEEEE tru

upper karma
#

Idk Im just like 13 so :/

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Oops wrong

summer barn
#

@serene field yeah thats prolly better lol

burnt relic
#

for the scale factor

#

is it 2.5/4.7=db/3

timber hinge
#

CB = 2, 2.5/2 = 1.25, 1.25 * 3 - 3 = 2.5

#

megathink wait

#

hmm looks right

#

mine

#

Idk what you're doing

burnt relic
#

lol same

serene field
#

<BAC: cos(t) = 3/sqrt(13)
Once you find t:
tan(t) = 2.5/x
Once you find x:
x - 3 cm = final answer

timber hinge
#

rEEE no trig needed

burnt relic
#

this has to be done without trig

summer barn
#

@burnt relic have you done sin cos tan yet

serene field
#

I like my trig GWfroggyAngryEyes

burnt relic
#

liek sin cos tan

summer barn
#

or do you know what they mean

burnt relic
#

i know

summer barn
#

oh ok use his method then

timber hinge
#

reeeeee similar 📐

upper karma
#

I forgot triggernometry since I did it last year XD

#

It's okay right?

burnt relic
#

its just that our teacher wanted us to do it with scale factor

upper karma
#

To forget u h

summer barn
#

@serene field but that requires a calculator right

serene field
#

If you're good enough with ratios, you don't need a calculator 🤔

summer barn
#

cuz you need to calculate t=arccos(3/sqrt13)

timber hinge
#

fishthonk gl with that

burnt relic
#

Ok i got one more

#

A plane takes off in a straight line and travels
along this line for 10 s, when it reaches a height
of 300 m. If the plane is travelling at 60 m/s, at
what angle is the plane ascending?

#

would i divide 300 by 10 to get the m/s to make all units the same?

mystic shadow
#

it's still the same problem

#

however you should see how far it travels by using its speed

#

$$\frac{60\text{ m}}{\text{s}}\cdot\frac{10\text{ s}}{}$$

somber coyoteBOT
mystic shadow
#

be sure to write units so you can cancel them correctly

burnt relic
#

Surveyors need to determine the height of a hill. They set up a laser measuring device on a pole that is 1m tall and shine the laser toward the top of a second pole, which is 1.6m tall. Then they adjust the distance between the two poles until the laser hits the top of the longer pole and the top of the hill. The 1.6m pole is 415m from the centre of the hill. The 2 poles are 12m apart. Find the height of the hill.

#

final q for the day if any1 can help

mystic shadow
#

draw the picture

burnt relic
#

solved

#

thanks for responding

mystic shadow
#

then draw a triangle eith the base starting from the top of the first pole

#

ok

#

similar triangles and all that stuff

river marsh
#

i propose we delete trigs from the entirety of human knowledge

#

because they are hard

last imp
dark osprey
#

,tex just use pyt similarty and find AD and then DB

somber coyoteBOT
last imp
#

Hey wut ?

dark osprey
#

the triangles are similar for obvious reasons 😄

#

similarty implies taht AB/AD = BC / DE

last imp
#

That's what I do

dark osprey
#

so its correct ...

last imp
#

Just proved it with trig

dark osprey
#

aah u were the one helping ;D

last imp
#

😟

upper karma
#

Does anyone understand Proofs?

mystic shadow
#

pretty sure someone exists that does

upper karma
#

But can you prove that?

#

i just need someone to explain ASA AAS and all the other ones

#

Those are generally considered postulates in elementary geometry, no?

#

I believe so but im in high school

#

That's what I meant. Between algebra last year and algebra ii/trig next year, right?

#

algebra 2 next year yes

#

OK, so in your level of geometry, I'm pretty sure SSS, ASA, and so on are considered postulates, no?

upper karma
astral hornet
#

you can prove similar triangle, then use prop of similar triangles

upper karma
#

Can someone explain to me how I go about solving question seven from above?

limpid basin
#

Have you learned transversals yet?

upper karma
#

Yes

#

@limpid basin

kind wagon
#

can anyone help me discover the third coterminal angle of angle 67?

split laurel
#

What do you have so far @kind wagon

kind wagon
#

@split laurel 427, 787

split laurel
#

why not just add 360?

#

1147

#

Or subtract 360

#

-293

#

@kind wagon

kind wagon
#

hmm cheers @split laurel

split laurel
#

anytime

copper valve
#

what

limpid basin
#

wat

steady sleet
#

ew geometry

pliant cloak
#

No geometry is fun

#

and combinatorial geometry is masterrace

upper karma
#

no geometry is fun. that's true, no part of geometry is fun

warm pine
#

And so began the great geometry war of discord

upper karma
#

Can someone help me with this question please

#

The graph of y=aSinb theta has a maximum value of 5 and a period of 45 degrees What are the values of a and B

#

since sin x has a maximum value of 1

#

max(a sin bx) = 5 implies that a = 5

#

the period is 45

#

45 degrees is pi/4

#

and regular sine has period 2pi

#

sin(kx) has period 2pi/k

#

so you can figure out b from that

#

Oh i see thanks

sacred cradle
#

@upper karma

upper karma
#

how do i prove EM=DM and EP=DP

wild hamlet
#

prove that ADB and BEA are similar triangles

upper karma
#

ADF?

wild hamlet
#

ADB sorry

upper karma
#

are they even similar

#

<A!=<B

#

i found that <EAH=<DBH 😄

#

<HCD=<HBM

#

<ECH=<HAM

lapis geyser
keen aspen
#

@lapis geyser sin function is odd and cos is even

lapis geyser
#

can you recommend a quick trig course online?

#

i need a refresher again

keen aspen
#

Hmm you can use Khan Academy

lapis geyser
#

ok thanks

sharp nymph
#

@lapis geyser Paul's notes

#

Very useful trig

lapis geyser
#

oooooh that looks like gold, thanks @sharp nymph

wild hamlet
#

Avoid posting in multiple channels

upper karma
mystic shadow
#

could you be more specific?

upper karma
#

like lets say i would want rotate this "T" about 50 degree how would i do that

mystic shadow
#

by the use of a rotation matrix

#

where the new coordinates (x',y') are given by multiplying the rotation matrix on the right by the original coordinates (x,y)

lapis geyser
#

can someone tell me yes, no if x = 4

hard gale
#

Ya x=4cm

lapis geyser
#

thanks

upper karma
#

@mystic shadow when doing only cos for x and sin for y it also works

mystic shadow
#

no it doesn't

#

if you can't do matrix multiplication, the full equations are:
x'=xcos(theta)-ysin(theta)
y'=xsin(theta)+ycos(theta)

upper karma
#

well i am doing

y = length * sin(rad(deg))
#

and it works fine

mystic shadow
#

you're just breaking the vector into its x and y components

#

not rotating it like your original request was

#

hope you figure it out bbl

young barn
#

what could be the graph of a two variable linear equation

#

like

#

y = m1x1 + m2x2 + c

serene field
#

That's a plane.

keen aspen
#

Yep

upper karma
#

if i know a position vector OA and another position vector OB

#

how do i know AB?

#

do i just add them

dire rampart
#

OB-OA

#

@upper karma

upper karma
#

ah i see

lapis geyser
#

can someone link me info i need to solve this please

umbral snow
#

Two things give most of these questions away
sin(-x) = -sin(x) (sin is odd)
cos(-x) = -cos(x) (cos is even)

#

@lapis geyser

mystic shadow
#

cos(-x)=cos(x)

lapis geyser
#

i never learned Trigonometry, learning it from scratch, and homework is due today, totally lost atm lol

#

any Khan series that explains the picture i linked. Pressed for time

#

after homework is due im going to go back over it again and study it further

dire rampart
lapis geyser
#

thank you very much both of you

upper karma
#

dudesmen

#

if the triangle with vertices X(3, 5) , Y(4, 2), Z(-5, a)

#

is right angled at Y

#

how can we find 'a'

#

?

hard gale
#

pythagoras will certainly do the trick

upper karma
#

how ?

hard gale
#

if our triangle is rectangle at Y, then

#

$$XY^2 + YZ^2 = XZ^2$$

somber coyoteBOT
upper karma
#

right

#

then ?

#

so i get the distance between the sides ?

#

and work my way backwards with the distance "algorithm"

#

?

hard gale
#

ya, and you'll get an equation for a

upper karma
#

the distance rule is as i know it something like this:

#

$$sqrroot((x2-x1)^2+(y2-y1)^2)$$

somber coyoteBOT
hard gale
#

yea get the lengths of the sides using dat formula

#

and plug them inside that pythagoras thing

upper karma
#

let me try and get back to you

#

bro

#

all i got is

#

XY = sqr10

#

XZ = sqr(64+(a-5)^2)

#

YZ = sqr(81+(a-2)^2)

#

where can i go from here

hard gale
#

yea seems right

#

ok so let's plug those things inside that pythagora's equation (we need those distances to verify pythagoras if we want XYZ to be a right triangle)

upper karma
#

XZ= sqr(YZ^2 + XY^2)

hard gale
#

$$XY^2 + YZ^2 = XZ^2 \iff 10 + 81 + (a-2)^2 = 64 + (a-5)^2$$

#

(tbh just leave the squares)

upper karma
#

there is no "(a-1)^2"

hard gale
#

typo'd

somber coyoteBOT
upper karma
#

"(a-2)^2" is the correct one

#

np

#

so i should move the 64 to the left and the (a-2)^2 to the right

hard gale
#

ya

upper karma
#

ok let me try

#

my bad math skills gave me:

#

-27 = -29

#

😂 😂 😂 😂

hard gale
#

oof

#

1sec brb

upper karma
#

ok

hard gale
#

ok so

#

moving our variables on one side and the constants on the other one

#

$$91-64 = (a-5)^2 - (a-2)^2$$

somber coyoteBOT
upper karma
#

mine is like

#

$$64-81-10 = (a-2)^2 - (a-5)^2$$

somber coyoteBOT
hard gale
#

yea exactly the same thing

#

(just the signs are reversed)

upper karma
#

ok

#

so the prob is with the next step

hard gale
#

expanding those squares :/

upper karma
#

for me it turned out like

#

:

#

$$-27 = a^2 - 4 - a^2 -25$$

somber coyoteBOT
hard gale
#

my eyes bleed

#

(a-b)^2 does not equal a^2 - b^2 in most cases

upper karma
#

wow!!!

hard gale
#

$$(a-b)^2 = (a-b)(a-b) = aa -ab - ba +bb = \boxed{a^2 -2ab+b^2}$$

somber coyoteBOT
upper karma
#

factorization ?

#

again!!!!!!!

#

no!!!

hard gale
#

that's distributing

upper karma
#

really ?

#

how do you do these things ?

hard gale
#

(that's what i just did?)

upper karma
#

so what should i do again ?

hard gale
#
  1. memorize it /or/ 2. remember that (a-b)^2 = (a-b)(a-b) by definition of squaring and expand
upper karma
#

hmm

#

gimme a sec

#

so basically it'll be

#

$$-27 = (a-2)(a-1) - (a-5)(a-1)$$

somber coyoteBOT
upper karma
#

right ?

hard gale
#

why a-1?

#

$$-27 = (a-2)(a-2) - (a-5)(a-5)$$

somber coyoteBOT
upper karma
#

oh sorry i was still stuck in the factorization thing

#

then ?

hard gale
#

then expand those

upper karma
#

how ?

#

if i did that i'll end up again in:

#

$$a^2 - 4 - a^2 - 25$$

somber coyoteBOT
hard gale
#

didn't think i'd be here for basic algebra but i am dommed to help you now

upper karma
#

bro sorry but i'm bad at math

#

like really bad as you can see

#

ughhhhhh

hard gale
#

$$(a+b)\cdot(c+d) = a(c+d) + b(c+d) = ac + ad + bc +bd$$

somber coyoteBOT
upper karma
#

bro ?

hard gale
#

so for example if we take $(a-2)(a-2)$

somber coyoteBOT
hard gale
#

$(a-2)(a-2) = a(a-2) - 2(a-2) = a^2 - 2a -2a + 4 = a^2 -4a +4$

somber coyoteBOT
upper karma
#

jaw drop really hard

#

how did you do that ?

upper moat
#

Distributive property

#

a * (b + c) = ab + ac
In this case, he expanded it into:
(a + b) * (c + d) = a * (c + d) + b * (c + d)

upper karma
#

aha

#

so in short....

#

black magic

upper moat
#

Well, here's an example:

#

4 * (5 + 6) = 4 * 11 = 44, yes?

#

Well, with the distributive property, this becomes

upper karma
#

yea i think so

upper moat
#

4 * (5 + 6) = 4 * 5 + 4 * 6

#

= 20 + 24

#

= 44

#

You basically multiply the stuff outside the brackets with everything inside

upper karma
#

but here we have 2 brackets and there is no outside

upper moat
#

Yes

#

But

#

(a + b) * (c + d)

#

Pretend (a + b) is ONE THING

upper karma
#

so basically

#

i think it'll be something like

#

$$-27 = a(a-2) - 2(a-2) - a(a-5) - 5(a-5)$$

somber coyoteBOT
upper moat
#

What was the original?

upper karma
#

$$-27 = (a-2) (a-2) - (a-5) (a-5)$$

somber coyoteBOT
upper karma
#

and the original to this is :

#

$$-27 = (a-2)^2 - (a-5)^2$$

somber coyoteBOT
upper moat
#

$$-27=a(a-2)-2(a-2)-a(a-5)+5(a-5)$$

somber coyoteBOT
upper moat
#

since -(a - 5)^2 = -1(a - 5)(a - 5)

upper karma
#

oh that's why the +

upper moat
#

yep

upper karma
#

but still why not the same with the 2(a-2) ?

upper moat
#

Because it's (a - 2)^2, not -(a - 2)^2

upper karma
#

oh ok

#

now how can i solve this "equation" ?

upper moat
#

Continue expanding

#

For example

#

a(a - 2)

#

Seem familiar?

#

a * (b + c)?

upper karma
#

NOOOOOOOOO!!!!

#

i can't expand more than that

#

like this is the best i can do

#

so...

#

a(a-2) will be a^2*-2a ?

upper moat
#

Yes

#

Gj

#

Now do that expansion like 3 more times

#

for the other 3 parts

upper karma
#

well it turned out to be at the end

#

that $$ a = -0.6$$

somber coyoteBOT
upper karma
#

is that right ?

#

ughhhh

plucky marlin
#

=pup -27 = (a-2)^2 - (a-5)^2

charred spearBOT
plucky marlin
#

did u mess up the signs or something ?

upper moat
#

-27 = (a - 2)(a - 2) - (a - 5)(a - 5)
-27 = a(a - 2) - 2(a - 2) - a(a - 5) + 5(a - 5)
-27 = a^2 - 2a - 2a + 4 - a^2 + 5a + 5a - 25
-27 = 6a -21
-27 + 21 = 6a
-6 = 6a
-1 = a

#

Was your process anywhere close to that?

bright nebula
#

-27=(a - 2 + a - 5)(a - 2 - a + 5)
-27=(2a - 7)3
-9=2a - 7
-2=2a
-1=a
shorter version

upper moat
#

That works, but i was talking to him about the distributive property above, so it was only fair to solve it the same way

dusky yarrow
#

absolutly aweful diagram here but this is the problem i have been presented with and i have no clue how to find the length of x or if it is even possible

umbral heron
#

try making triangles with the center of the circles

dusky yarrow
#

o

#

thats genius

umbral heron
#

lol

dusky yarrow
#

ty

umbral heron
#

np

dusky yarrow
#

ok now im stuck again

#

how would i find the hypotenuse

thorn talon
#

which triangle did you make?

dusky yarrow
#

lemme make a new better diagram

thorn talon
#

i assume the right triangle?

#

with the hypotenuse through the two circles?

dusky yarrow
#

not better but yeah that triangle

thorn talon
#

there's a better triangle you can draw i think

#

that vertical side

#

how about you extend it further?

#

so it goes down to the centre of the bottom circle

dusky yarrow
thorn talon
#

yep

#

like that

#

do you know the length of each side now?

dusky yarrow
#

no

thorn talon
#

well the vertical one is 1 + x right?

dusky yarrow
#

yes

thorn talon
#

top horizontal is 1 right?

dusky yarrow
#

yes

thorn talon
#

and the hypotenuse

#

it's equal to 2 radii length right?

dusky yarrow
#

im not sure what radii is

thorn talon
#

2 radius length

dusky yarrow
#

oh yeah

thorn talon
#

so 2 * 1 = 2 right?

dusky yarrow
#

yes

thorn talon
#

and then you can just pythagorean theorem from here

dusky yarrow
#

alright thank you

lusty maple
#

Would I be right in saying that given 2D vectors A and B, if (A + B)'s x and y components are both not zero, A * q added to B * p can be equal to any 2D vector by changing values of q and p (allowing q and p to be negative, zero or positive)? If that makes sense to you.

hard gale
#

what if A and B are collinear ? thonkeyes

lusty maple
#

if (A + B) has non-zero x and y components then wouldn't they inherently be not collinear?

#

or am I understanding you wrong

hard gale
#

A=(1,1) / B=(2,2) they're collinear right?

lusty maple
#

ah I see, I only thought of them pointing in opposite directions. Good call

#

So would A + B and A - B and B - A all have to have non-zero x and y components?

hard gale
#

well you'd need A != kB for any k in R

#

(which is much more cases than you can write in a "A+B A-B" way)

lusty maple
#

All right, makes sense.

#

And in 3D I'd need 3 vectors?

hard gale
#

non colinear one another again but ye

lusty maple
#

That's great, thank you. I'm working on a programming project and want to balance a mass on thrusters automatically, or at least attempt to get as close to it as possible.

#

Maybe a physics server might be a better place for assistance with the rest of it though

hard gale
#

oof good lucks : if you wanna go further about this vectory idea just take any lin alg book

#

yeah physics would be better ^^

lusty maple
#

Thanks once again, I appreciate the help 😃 I'll keep at it

hard gale
lusty maple
umbral snow
#

You want to look into control theory for holding a state

#

Feel free to ask anything about control here or in the physics server!

lusty maple
#

Currently I'm at the point where I have the torque that each thruster provides and can also get the change in angular velocity for firing it for one physics update (1/50s), my approach is to give each thruster a factor from 0 to 1 based on how (inversely-)"useful" it is to correcting the error. So the more torque a thruster has (if it is acting in the correct direction) the more useful it is therefore it needs to be at a lesser throttle % (factor) than a weaker thruster to generate the same torque on the centre of mass.
If I'm thinking it through right, assigning each thruster a factor based on the amount and direction of torque produced so that the torque * factor are equal for all thrusters should produce a balanced system.

#

My problem is calculating the usefulness properly. I tried a couple approaches and some worked a bit but not fully. Best I had is a stable balancing system but it would constantly switch between two engines firing at full power and two being off, so whenever it would lean any amount to the left of centre the right engines would turn off and vice versa. I tried fixing it by making the error-based factor smaller the closer to the correct orientation the object was, so if you were 45 degrees off the engines would try hard to correct it but as you approached the correct orientation the factor would fade towards one which simply has all the thrusters balanced proportional to how much torque they produced. I messed up somewhere and couldn't get it right though and anyway it felt like an improper cheaty solution.

#

How would you approach a problem like this:
vectors t0 through tn are known (torque from thrusters)
coefficients c0 through cn are unknown (factors or throttle, but for the sake of this they are not constrained to 0.0-1.0, they can be any real number)
error to correct e is known

find values of c0 to cn where (c0t0 + c1t1 + c2t2 + .. + cntn) is as close to e as is possible

there would be multiple answers I assume and that makes it even harder. Is there a better approach to something like that? Where would I find info on this?

serene field
#

Something like

somber coyoteBOT
serene field
#

That?

lusty maple
#

yes, although that wouldn't cover edge cases where they can not be equal to e and instead you'd have to get the closest approach

#

Would they need to be broken down into simultaneous linear equations recursively? Ignoring the edge cases for now

serene field
#

Honestly, I have no idea. A linear system is probably the way I'd attempt to solve this. Maybe one of the helpers can solve this better than I know how. 🤔

lusty maple
#

That's grand, I'll look into the different methods. Thanks 😃

lusty maple
#

A lad on a computer science discord said that it's a least squares problem but I can't see any way to use the method for my problem although I do see some similarities

lusty maple
#

Now that I think about it, I'm pretty sure I can't break it down into linear equations because even if it was 2(c0) + 3(c1) = 4, there are infinitely many values for c0 and c1 that would work. The only values I actually want are where |c0-c1| is the smallest it can be.

#

Maybe I should think of it as a line on a n+1 dimensional graph

#

If that would get me anywhere closer to an answer? Probably not but worth to think on

#

e.g. say error correction value e is the y axis, c0 is x axis and c1 is z axis. Using the previous example, y = 4 so equation is 2x + 3z = 4.

umbral snow
#

Okay, so what is this thing? Are we in 2D? A plank with two forces acting on each side?

lusty maple
#

My ideal result would be where x and z are the closest and I know it's easy af to calculate that but it's late and I can't put my finger on it lol

#

It's 3D

#

Imagine a hovercraft with engines

umbral snow
#

Four of them?

lusty maple
#

for example 1 each corner so 4 engines

#

yea

#

And ideal scenario would be all 4 at 100%

#

but a possibility would be 2 corner engines at 100 and 2 others at 0

#

and it would still technically be stable

#

so I guess total % should be max if I'm thinking straight

#

either that or all %s should be as similar as possible

#

I'm leaning towards the latter actually

#

Also important to note is that in this example the engines are all pointing straight down so it's more 2D-ish but that may not always be the case

umbral snow
#

I imagine you're trying to control two things, the height of the hovercraft and the angle at which it hovers

#

3D manouvering is tough, lol.

lusty maple
#

The height would be easier I assume

#

get the angle right then adjust total thrust

#

so getting the angle stable is the main challenge

umbral snow
#

You can do both at once with an ideal system

lusty maple
#

How is that?

umbral snow
#

Well, how much do you know? Understand calculus?

lusty maple
#

Not really just the overall idea of it, not in uni yet so just doing this as a hobby out of interest

#

I have the vague idea of getting the slope of a curve by being more and more precise with an average over a time, or however you would put it. But in-depth not at all

umbral snow
#

In physics, velocity is the slope of displacement, and acceleration is the slope of velocity

#

You also have F = ma, so you can control "a" directly with thrusters.

So you have full control over acceleration, but you want control over displacement.

lusty maple
#

So I imagine there'd be a most efficient way of changing s by controlling a, since if you just go full on until you overshoot you're gonna have to backtrack etc?

umbral snow
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Exactly, you're calling it. And, it's not a crazy simple problem

lusty maple
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And how does that play into angle?

umbral snow
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All the while, you have to control the angle

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You have Newton's second law of rotation.
τ = Iα

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τ, or torque, is controlled by the thrusters, so you can control acceleration of angle, or α

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Once again, you want to control the angle, but you have control of the second derivative

lusty maple
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ah, I see

umbral snow
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So I've said a lot but haven't said much for results

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You should have some I from the physics simulation, so you should know how fast it starts to rotate, given a thruster is on

lusty maple
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Yeah, I can get the angular acceleration (if that's the word) for firing it for 1/50th of a second (one physics frame), I assume that dealing in discrete units of time simplifies things as well compared to a real-world simulation.

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I could be wrong through since that may only be the case if you are doing compounding calculations (or however they're called)

umbral snow
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Run one thruster for two "cycles", how much does the angle change in each one?

lusty maple
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angle or angular velocity?

lusty maple
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Angular velocity changes almost same amount as predicted by the code, so for x axis it's about 7.5 deg/s per cycle. Angle itself is more difficult because the whole thing flies off at an awkward rotation and direction so the axes get messed up, since I know ang vel around local axes but the rotation itself is shown about the global axes. I use unity and the physics tend to be a bit wonky but realistically implemented. My money is on local x angle being 0 at beginning, then 1/50 of 7.5, then another 7.5 is added to vel so 1/50 of 15 added to angle so total after 2nd update would be 7.5/50 + 15/50 = 22.5/50
Phys frame 0: angle 0 vel 0
1: angle 7.5 vel 7.5
2: angle 22.5 vel 15

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I'd have to do a more in depth test for 100% accurate results, I through that one together sloppily since it's 3am so I'll be back at it tomorrow. Thanks a lot for the insight btw, sorry about running off partway through but I shouldn't be messing up my sleep more than already lol. I'll check back the next day

lusty maple
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Before I forget though, if I wasn't dealing with vectors but instead scalars, having an equation e = c0t0 + c1t1 etc. Wouldn't be hard to get optimal values for. I believe it would be:
optimal coefficient = error correction amount * (1 - (torque/total torque))
including signs and so on, not absolute values. Ofc if total torque cancelled out by default then it would be dividing by zero, so I'd have to have a failsafe for that and just set them all to one. That's besides the point though. My problem is that in 1D, A = kB no matter what, for real numbers. In 3D though, it's much more complex. Also torque can be in the wrong direction and in 3D that is usually not solveable by scaling, hence why my initial question where it was deducted that you'd need 3 vectors which would not be collinear to have full control over where they point if scaled independently and summed.

surreal bolt
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Hello!

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Question 1: So you have an 8 inch x 8 inch standard issue chessboard. You are also provided with unlimited 2 inch x 1 inch rectangles (dominoes).

Can you tile the chessboard with the rectangles with no overlap and no extra rectangles nor parts of rectangles hanging off the playable part of the chessboard?

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SPOILER

Turns out the answer is yes. Just tile each row with four 2 x 1 rectangles end to end.

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The following a famous problem ...

Question 2: So you have an 8 inch x 8 inch standard issue chessboard AND you remove 1 pair of diagonally opposite corners. You are also provided with unlimited 2 inch x 1 inch rectangles (dominoes).

Now, can you tile THIS chessboard (with corners removed) with the rectangles with no overlap and no extra rectangles nor parts of rectangles hanging off the playable part of the chessboard?

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SPOILER

It turns out ... no :(

But, of course, in math you need proof.

And this turns out to be a tricky proof to come up with, but very simple to understand.

Each rectangle MUST cover two squares: one square of each color.

Since the two removed squares are the same color (WLOG black) you have 32 white and 30 black squares left over. This cannot be tiled by 2 x 1 rectangles.

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But then one has to ask ... Question 3: What about other shapes? Maybe Tetris shapes?

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Of course you can't tile an 8 x 8 chessboard with two corners removed and have it be tiled by pieces with an area of 4. That's 62 for the leftover area and 4 doesn't divide 62. 😃

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Question 4: But what if I said you can remove Any 4 squares of the same color? Or any 4 squares where 3 are of one color and 1 is of the other? We solved the problem of not having the whole area being divisible by the area of the piece.

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It turns out that all of these Tetris pieces:


++  ++      ++  +++ +
++ ++  ++++  ++   + +++

... must also cover exactly 2 white and exactly 2 black squares.

This means that not just any one of the above Tetris pieces but Any Combination of pieces cannot tile any board with unequal white and black squares. The only odd piece out is the T-shaped piece. But I'll leave that for further study.

weary ingot
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Hey guys what is the best book for trig, a book.that explains concepts, and gives examples, easy to understand. Overall a great book to learn trig

upper karma
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how do you sketch this graph with just the function and A values? thanks 😃

waxen gorge
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Take the derivative

vital frost
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So do I have just have to draw it and explain right?

glad ocean
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yeah I guess

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for AA postulate, say that:

  1. the sum of angle measures in a triangle is 180 degrees
  2. say there are three angles in two triangles: in triangle ABC, There are angles 1 2 and 3 and in triangle DEF there are angles 4 5 and 6
  3. given angle 1 is congruent to angle 4 and angle 2 is congruent to angle 5, angle 3 is congruent to angle 6 using the difference of 180 - (angle 1 + angle 2) = 180 - (angle 4 + angle 5)
  4. since this is AAA, the ratios of the corresponding sides in each triangle
  5. in conclusion, AA postulate is an extension of AAA, proving that two triangles are similar
azure tundra
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a. since ADC is a right angle at D, ACD (angle) = angle B (since they both equal 90-A) therefore (by AAA similarity) ADC is similar to ABC, same thing for CBD but this time it's angle DCB=90-B (aka same as A)

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hopefully this helps (sorry for the amateur proof writing)

weary ingot
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Standard form of a circle is (x-h)^2+(y-k)^2=r^2,let's say center of the circle is at 3,-2. Now its (x-3)^2+(y+2)^2=81, for what type of question would they ask me to plus in x and y Into there and what does that give me?

vital frost
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I'm so confused what

glad ocean
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X + y = 10

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oh wait 81 should be the sum of two squares

vital frost
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Are y'all talking to me?

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@keen aspen since you really helped me.last time can you help me with the picture above

glad ocean
copper valve
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no

glad ocean
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all the lines that you can make out

copper valve
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no

surreal bolt
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use excel --> save delimited --> get rid of all commas ....

vital frost
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Help...

umbral snow
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Which are you having trouble with? Any definitions you're not good on?