#help-0

1 messages Ā· Page 247 of 1

ebon sparrow
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no number given

primal flume
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hypotenuse

ebon sparrow
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yeah i know but like i dont see any number

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on this picture

primal flume
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ok

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both adjacent and hypotenuse

ebon sparrow
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oh

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you need to use cos

primal flume
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so cos(x) = 5.5/4.5?

ebon sparrow
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$cos(\theta) = \frac{4.5}{5.5}$

ocean sealBOT
primal flume
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oh

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is that it?

ebon sparrow
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yes

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you need find the theta

primal flume
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0.8181818181818182

ebon sparrow
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now use cos shift

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$cos^{-1}$

ocean sealBOT
ebon sparrow
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this ^

primal flume
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i dont know what that is

ebon sparrow
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thats why you need find the angle

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you use shift

primal flume
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im confused

ebon sparrow
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do you have a calculator?

primal flume
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yes

ebon sparrow
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wait let me show you

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those things are called arsin, arcos and artan

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you need to use this to find the theta

primal flume
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mhm

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so what do i do?

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cos to the power of negative 1?

ebon sparrow
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can i see your calculator

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there should be a shift button

primal flume
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its a casio

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yep

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there is

ebon sparrow
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yeah use this

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like this

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since it's 35.09 it should be 35.1

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that works

primal flume
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yep

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i got that too

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on my calculator

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so thats the answer?

ebon sparrow
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yes

primal flume
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wait i got 38.99644581

ebon sparrow
primal flume
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yes

ebon sparrow
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if you're using a real calculator by hand then you gotta type it like this $cos^{-1}(0.8181818181818182)$

ocean sealBOT
ebon sparrow
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then it gives you 35.09

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or 35.1

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do you remember this?

primal flume
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sorry im trying to find my phone so i can send you a photo

ebon sparrow
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okay

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you can use online calculator though

primal flume
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nvm my calculator has been wrong before

ebon sparrow
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oh I see

primal flume
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so 35.1

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ok

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so

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i have one left

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one question left

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then i can go to sleep

ebon sparrow
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oki

primal flume
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its this

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but i need to use multiplication to figure it out

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not division

ebon sparrow
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I feel like this is the same question

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you asked for the first place

primal flume
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yes

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but you told me how to figure it out using division

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didnt you?

ebon sparrow
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you because you were finding for H

primal flume
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...

ebon sparrow
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this

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you said x was unknown

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so

primal flume
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my brain isnt working

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is it okay if i ask you tomorrow?

ebon sparrow
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on what

ebon sparrow
primal flume
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will you be on in 12 hours?

ebon sparrow
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it's 10am for me

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if 10 hrs more

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then 10pm

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yeah I can

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you can dm me or ping

primal flume
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k cuz its 12am for me and im tired

ebon sparrow
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damn I feel you

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I think it's time to rest

primal flume
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yeah i was up earlier to do research on a battle for history

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now my desk is covered in paper and books

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mmm

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ok so ill hopefully talk to you in like 12 hours

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maybe earlier

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goodnight

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or goodday

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idk

ebon sparrow
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good night

primal flume
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bye

ebon sparrow
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it's morning for me

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10am

primal flume
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oh yeah

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well have a good day

ebon sparrow
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thanks

lone heartBOT
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@primal flume Has your question been resolved?

lone heartBOT
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tawdry urchin
#

Assuming tan(a) - tan(b) = x, and cot(b) - cot(a) = y, find cot(a-b) in terms of x and y.

tawdry urchin
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I know that cot(a-b) = 1+tan(a)tan(b)/tan(a)-tan(b)

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so it is $\frac{1 + \tan a * \tan b}{x}$

ocean sealBOT
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dork9399

slender gull
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You can find tan(a)tan(b)

tawdry urchin
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but now what should I do?

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how?

slender gull
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rewrite cot(b)-cot(a) in terms of tan

tawdry urchin
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thanks

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.close

lone heartBOT
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shadow sparrow
#

Back at it again with the basic mathematics, I'm not seeming to remember how to solve this, for some reason.

shadow sparrow
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$\frac{-3}{4}+C=2$

ocean sealBOT
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huntifer

mellow grail
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yo

shadow sparrow
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Is it not multiply the reciprocal of the fraction by both sides?

mellow grail
shadow sparrow
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Ah, so its not using reciprocals here?

mellow grail
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no

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thats when the variable is multiplied by something

sharp thorn
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solving for c?

shadow sparrow
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Ahhh.

shadow sparrow
sharp thorn
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try adding 3/4 on both sides

mellow grail
shadow sparrow
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I see what you're saying, make it 0/4, which is 0.

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And in this instance its 2+3/4

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which is actually 8/4+3/4

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So its then 11/4

mellow grail
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yep

shadow sparrow
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That makes a lot more sense

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I was sitting here like

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"Reciprocal not comprende?"

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So if addition, get rid of fraction with addition, if multiplication by the variable, get rid of fraction with multiplication

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and if its division, use the fraction rules

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Cool, thanks lots!

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.close

lone heartBOT
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cosmic coral
#

Here, in the circle, RS = SM = 6 units. Radius of the circle equals to 5 units. Find RM. Feel free to ask if anything's unclear, the drawing may be a bit shabby. Try not to use too advanced math(not above trig). Thanks.

gray isle
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what have you tried?

lone heartBOT
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@cosmic coral Has your question been resolved?

cosmic coral
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but then i couldn't figure out anything

gray isle
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draw a line from O to P

cosmic coral
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yeah i did that too

gray isle
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introduce a variable like x for OP for convenience

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PS can be expressed in terms of x

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OM is a radius, so also has length 5

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an expression for PM can be obtained from both right triangles

cosmic coral
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i see

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then we can do 2PM and find RM

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but is there a way to get a real value?

gray isle
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an expression for PM can be obtained from both right triangles
set those two expressions equal to each other to determine x and hence PM

cosmic coral
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ohh

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then it's solved?

gray isle
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if you do what's been outlined, you'll get the result

lone heartBOT
#

@cosmic coral Has your question been resolved?

lone heartBOT
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autumn mountain
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is it possible to do smth to this using quadratic formula

mortal trellis
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its a quadratic in h, so yes

autumn mountain
mortal trellis
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this is mostly just an exercise in keeping things organized

autumn mountain
mortal trellis
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if you have it written down on a paper, it might help to eg mark all the terms that have h^2 in them in red, all those with just h in blue and the rest in green

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or by underlining them in three different ways or something

autumn mountain
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gotcha

mortal trellis
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what you want to do in the end is to get (some long expression)*h^2 + (other long expression)*h + (third long expression) = 0

autumn mountain
mortal trellis
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do you know how to use the quadratic formula on eg 7h^2-13h+27=0 ?

autumn mountain
mortal trellis
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then here its the same just that the numbers look uglier

autumn mountain
mortal trellis
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cot(56) is just some number

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you could calculate it with a calculator if it bothers you

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(although that will introduce rounding errors)

autumn mountain
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i see

autumn mountain
mortal trellis
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ok

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what do you have currently

autumn mountain
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100cot^2(56)+sqrt (-100cot^2(56))^2-4(cot^2(56))(2500cot^2(55))

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all over 2cot^2(56)

mortal trellis
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no

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you ignored the right side

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you have to bring everything to the left side before you apply the quadratic formula

autumn mountain
autumn mountain
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i see

autumn mountain
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the 2(61)(hcot55 thingy

mortal trellis
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multiply out the bracket

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then you have one term with h and one without

pine grove
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what the

autumn mountain
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wait nm

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nvm

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i just times it by both

mortal trellis
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yes

gilded mortar
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how much is 2+3?

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it's 6 am i right?

mortal trellis
gilded mortar
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but I don't trolling, I really dont know

ornate ginkgo
gilded mortar
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23

vale wigeon
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dont interrupt somebody elses

autumn mountain
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gimme a sec

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the top one

mortal trellis
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,rotate

ocean sealBOT
autumn mountain
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oh and -61^2

mortal trellis
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that looks good

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unless I missed something

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now you can factor h^2 out of the first two terms and h out of the next few

autumn mountain
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ohh

mortal trellis
autumn mountain
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yup it does

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i have -h at the start of the second group but is that ok

mortal trellis
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-h*(expression) = h*(-expression)

autumn mountain
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should i switch it

mortal trellis
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your choice

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not necessary as long as you treat it correctly in the next steps

autumn mountain
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i will just in case

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so once i've done that

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then what do i do

mortal trellis
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now you can apply the quadratic formula

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although at this point it would probably be fine to first calculate these long expressions, shouldnt introduce too much rounding errors

autumn mountain
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Tryna do that now

mortal trellis
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I have to go now but you can definitely finish it from here

autumn mountain
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Oki

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Thx for the help

lone heartBOT
#

@autumn mountain Has your question been resolved?

autumn mountain
#

Yes

lone heartBOT
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junior warren
lone heartBOT
junior warren
#

can anyone let me know if this statement is somehow true, pulled this out on a midterm and got full marks

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but it was a complete guess as i was stuck

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so just interested in knowing if this step specifically has any merit

trim sorrel
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What is the statement

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?

junior warren
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the ms paint writing

trim sorrel
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What are A and B

junior warren
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ah

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i knew how to find the inverse but couldnt come up with anything quick

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to prove it was invertable

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and i just dont see my statement having any correlation to invertability

trim sorrel
#

Ngl i dont see how it connects either

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Let me think some more

junior warren
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im thinking it mustve been a marker error

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we got these back in a day so its likely they just let it slide lol

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fierce narwhal
#

yo can anyone help me with this

lone heartBOT
fierce narwhal
#

don't know how to start

fossil latch
#

Let's change it to cos²x first, shall we, since x -> Ļ€/2 and sinx becomes 1, not 0

fierce narwhal
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alright

fossil latch
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I also hate how it's sin²2x instead of being with sinx and cos x

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Have you learnt the trig identity sin2x= 2sinxcosx?

fierce narwhal
#

i learned that like 20 mins ago

fossil latch
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Okay then you know it :D

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So finally the limit equation becomes 4cos²x sin²x / cos²x

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This limit is now much more solvable

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That's it

fierce narwhal
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yeah i can see it now

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wait can you explain how it becomes 4 cos^2x sin^2x

fossil latch
fierce narwhal
#

šŸ‘

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thanks

fossil latch
#

General tip: if you see + or - signs on fractional limits you generally want to consider factorising or changing into more favorable terms

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Especially for trigs.

fierce narwhal
#

.close

lone heartBOT
#
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frosty sparrow
#

how can i prove that if x² is a multiple of 3, then x is a multiple of 3

frosty sparrow
#

i thought about doing it using a contradiction, but how can i express that a number can't be divided by 3 mathematically?

echo socket
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Considering the cases x = 0, 1, 2 (mod 3) is one way

frosty sparrow
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yep

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but how can i demonstrate this?

echo socket
#

thonk Just show that x^2 = 0 (mod 3) happens only in the first case, meaning x = 0 (mod 3) must be true

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Meaning x is a multiple of 3

frosty sparrow
#

ohh got it

#

thx

#

.close

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barren portal
lone heartBOT
barren portal
#

I didn't get why they said r cong to r-9 (mod 9)

worn fox
#

You don't get why it's true or you don't know where they've used it?

barren portal
#

I couldn't understand the solution, my reasoning is that, set of possible least residues modulo 9 are {0,1,...8}

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so x^2, has to be square congruent to square of each of them

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resulting in x^2 cong to {1,4,7,9} (mod 9)

worn fox
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Where did you get 3 from?

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Right, that's the same as they're doing

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Just that they've used for example that 7 = -2 mod 9

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To make calculations easier (not that they're overly difficult without)

barren portal
#

why is it +- ?

barren portal
#

they didn't do the sepearetly right?

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as in they didn't compute 5,6, 7, 8, but rather used that fact 5 mod 9 is cong to -4 mod 9

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similarly for others

worn fox
#

Yes

barren portal
#

thank you

#

.close

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night lodge
lone heartBOT
night lodge
#

how do we get 1/2 here?

alpine sable
#

divide both sides by A_0

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as said on the image

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well, the original 1/2 gets here

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because you are finding the half life

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(A_0)/2 is half of the original amount

night lodge
#

ohhh okay

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ty that rlly clears it up

alpine sable
#

np

night lodge
#

.done

#

.close

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weary wyvern
#

for the covariance of 2 rvs to be defined, do they need to be on the same probability space?

lone heartBOT
#

@weary wyvern Has your question been resolved?

marsh rapids
#

surely, they ought to be otherwise you can't take the expected value of their product

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E((X-E(X))(Y-E(Y))

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E(XY) - E(X)E(Y)

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either way you need XY to be defined and to be able to take the expected value of that, so you need a common probability space

weary wyvern
#

makes sense

lone heartBOT
#

@weary wyvern Has your question been resolved?

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patent swallow
lone heartBOT
patent swallow
#

hint plz šŸ˜„

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I can share what I did but I'm getting into problems

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I need to find fx

vale crag
#

hint comes after

patent swallow
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ok

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uploading

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its tricky

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I tried this but it wont help I guess

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since dt is dividing

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and then to the right you can see my last attempt

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and it doesnt look right at all

vale crag
#

alright yea you seem kinda lost

patent swallow
#

indeed

vale crag
#

this one actually seperates quite nicely

patent swallow
#

I guess I need to get f'x/fx and integrate both sides

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but yeah no luck yet

vale crag
#

try factoring all the f'(x) together

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at the start

patent swallow
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so 5f'x to the other side first

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right?

vale crag
#

ya

patent swallow
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going

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ok done

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ah

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ok lemme see if I can do it now

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finishing

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1 moment

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doesnt look good either 🤣

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is this right? šŸ¤”

vale crag
#

how did you integrate the left hand side ?

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seems very wrong

patent swallow
#

wow

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why

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where

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šŸ¤”

vale crag
#

it sounds like you split your fraction by the denominator to integrate your function

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but fractions don't work like that

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you're not an algebra 1 student in disguise aren't you?

patent swallow
#

bruh

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right

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yeah fucked up mistake just saw it lmao

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hahahaha

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thanks I'll re-do it šŸ˜„

lone heartBOT
#

@patent swallow Has your question been resolved?

lone heartBOT
#

@patent swallow Has your question been resolved?

lone heartBOT
#
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dapper lynx
#

Hey all

lone heartBOT
dapper lynx
#

The original text of the question

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Is it asking this, paraphrased?

worn fox
#

that is what it is asking yes

dapper lynx
#

Awesome

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XD

#

Math with teachers for whom English is a second language can be tricky

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I've lost more than a few marks over the terms

#

.close

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proven leaf
#

Khan Academy and YouTube are good online places to independently study mathematics :) that's how I started but there are many ways to approach

foggy current
#

I'd suggest the basic algebra section on Khan Academy

alpine sable
#

what have you studied so far/

foggy current
#

Or if you want to get more basic, pre-algebra might be good

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Yes

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There's also the section 7th grade math, which also may help

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Because math is not just algebra

alpine sable
#

Does anyone know how to do this if so can u show me the details how it's done plz

lone heartBOT
#

@alpine sable Has your question been resolved?

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icy jewel
#

idk what i did wrong for the domain

lone heartBOT
crisp cargo
#

can x be less than -2?

icy jewel
#

oh

#

im blind

#

i had brainfart

lone heartBOT
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icy jewel
#

.close

alpine sable
#

Wait what

#

Shouldn't the domain be (-infinity,1 ]n[1,infinite)?

crisp cargo
#

nah

alpine sable
#

what is the answer?

crisp cargo
#

[-2,infinity)

#

weird that the chat doesn't close

alpine sable
crisp cargo
#

look at the piecewise definition

alpine sable
#

Oh yeah sorry my bad šŸ˜†

#

The graph was confusing

lone heartBOT
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quick gust
#

Hello could someone check this for me : )

lone heartBOT
shy dove
#

yeah they look fine

quick gust
#

Coolio thankyou

#

.close

lone heartBOT
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snow salmon
#

anyone have all formulars for y11 GCSE

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grave eagle
#

whats the difference between

lone heartBOT
grave eagle
#

-f(x)

#

and

#

f(-x)

#

i just realized how stujpid the question is nvm

long axle
#

Lol

#

U got it?

grave eagle
#

i mean yeah

#

but im stil stuck

#

i get what the difference is but im lost here

#

i just need some more thinking give me a sec

#

i have no idea

torn elk
#

which one u don't know?

grave eagle
#

all below f(x-1)

torn elk
#

read the first f(x) till the end

#

and if you know what's f(-x) you'll be able to solve it

#

here's an example

grave eagle
#

y axis flip

#

i see that

#

so (x-1) is supposed to change the x value

#

by +1

#

doesnt that mean that y is unaffected??

trim sorrel
#

You want to find f(x - 1) when x = -1

#

so whats x - 1

grave eagle
#

-2?

#

ohhhhh

trim sorrel
#

Right

#

So you want f(-2)

#

For that one

#

Its just a matter of plugging things in

grave eagle
#

OH

#

F(-2)

#

not 02

#

-2

torn elk
#

for -1 it's f(-2)

grave eagle
#

so just type f(-2) in

torn elk
#

which is

grave eagle
#

the key says the answer was 1?

torn elk
#

you can see here

grave eagle
#

O

#

OHHH

#

do they all go back

#

had to get a new one since i got the other one wrong

trim sorrel
#

Yeah you have to reference the original function values

grave eagle
#

so here

#

-4-1

#

=-5

#

thres no -5

trim sorrel
#

Hm?

grave eagle
#

on x's

trim sorrel
#

f(x - 1) when x = -1

#

f(-2)

grave eagle
#

bruh

#

ok

trim sorrel
trim sorrel
#

?

#

Did you confuse it with this box

grave eagle
#

absolute brainfart

#

my bad

trim sorrel
#

Lolll

#

You got it now tho

grave eagle
#

ye

#

im a math god

#

thanks

trim sorrel
#

W

lone heartBOT
#

@grave eagle Has your question been resolved?

lone heartBOT
#
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lone heartBOT
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kind wind
#

For question 4

lone heartBOT
kind wind
#

i cannot seem to solve it for a reason

#

quadratic formula and man does not work

#

caculate the angle that a line with a slope of 4 makes with the x-axis

#

another question i do not understand

trim sorrel
#

Do you know about the discriminant

#

Oh wai

#

It asks for the actual zeros not number of zeros

#

Sorry misread

#

Why doesnt quadratic formula work?

#

Oh does it mean to say x^2 - 2x + 24 it might be cut off

lone heartBOT
#

@kind wind Has your question been resolved?

kind wind
#

_4ac part

#

-4ac

#

it is a negative under a root so my calculator keeps saying math error

trim sorrel
#

Right

#

Can you take the square root of a negative number?

trim sorrel
#

Right

kind wind
#

gives me like -59 or someting

trim sorrel
#

(You actually can, but you'll learn that later)

#

Anyways,

kind wind
#

so how do i get the zeros

trim sorrel
#

What that means is that the quadratic equation produces invalid values

#

This means that there actually are no zeroes

kind wind
#

u sure

#

u tried it?

trim sorrel
#

x^2 - 2x + 24?

#

Right?

kind wind
#

yes

trim sorrel
#

Assuming you havn't learned about complex numbers, then yes there are no zeroes

kind wind
#

yeha

#

yeah

#

ok thats makes sense

trim sorrel
#

šŸ‘

kind wind
trim sorrel
#

You gotta use trig

kind wind
#

i dont know how to apply slope tho

#

like if it gives me a side length or something maybe i can get the angle

#

it confuses me

#

this is what i have

trim sorrel
#

What's an equation of a line with slope 4

kind wind
#

4/1

trim sorrel
#

Equation of a line

trim sorrel
#

Nvm

#

So slope = rise/run right

#

4/1

kind wind
#

yes

trim sorrel
#

That means that for every increase of x by 1, y increases by 4

#

Think about how that fact can give you a triangle

kind wind
#

i dnot understand

kind wind
#

and its not giving me triangle

trim sorrel
#

Youre like almost there

#

Take one of those points

#

Like (1, 4) for example

kind wind
#

ya

trim sorrel
#

Take the origin

#

And take (1, 0)

#

You get a triangle

kind wind
#

ohhhhhh

trim sorrel
#

A right triangle

#

With side lengths you know

#

Or at least you know two of them easily

lone heartBOT
#
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trim sorrel
#

And then use trig with the angle

kind wind
#

just tan

#

right

trim sorrel
#

Right

lone heartBOT
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kind wind
lone heartBOT
kind wind
#

.closed

#

.close

lone heartBOT
#
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glass onyx
#

Is possible to evaluate value of trig functions like sin(76.2) etc without calculator

glass onyx
#

And arctan arcsin arccos?

vapid shuttle
#

it is possible

#

why are you asking though?

glass onyx
vapid shuttle
#

depends on the angle

glass onyx
#

It can't get values like 67 72.4 etc

median oar
#

you can do series expansion

vapid shuttle
#

there are ways to get those values approximately without using a calculator, but it is difficult. Why are you asking?

median oar
#

you can solve it numerically like calculators do

glass onyx
vapid shuttle
#

of course angles that are on the unit circle, or near angles on the unit circle, that is not so hard

vapid shuttle
#

in case...??

#

in case all calculators and tech in the world get fried and you must know the exact value of arcsin(72.4)?

median oar
#

nah it's a valid question to ask how to numerically approximate something like that

sour dove
# vapid shuttle in case...??

just wait until robot overlords take over all technology. Then we'll be happy we know how to find sin(76.2) by hand

vapid shuttle
#

(I'd say if it was a valid question, the reason would have to be more valid than "just in case", but I digress lol)

lone heartBOT
#

@glass onyx Has your question been resolved?

lone heartBOT
#

@glass onyx Has your question been resolved?

lone heartBOT
#

@glass onyx Has your question been resolved?

lone heartBOT
#
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scenic wing
#

how did they solve it when inside the root is negative

outer kite
#

uh

scenic wing
#

49-196=-147

outer kite
#

so it's root(-147)

#

which

#

using index laws

#

is root(-1) times root(147)

#

root -1 is i

scenic wing
#

root of 147 is 12.124

#

what did they simplify it to

#

wait

outer kite
#

firstly do you get the i part

scenic wing
outer kite
#

if so then 147=7x7x3

#

so you take make it root(49) times root(3)

#

root 49 is 7

#

I can write out the working out if you want

scenic wing
#

root of 49 simplifies to 7

#

how did it disappear

outer kite
#

it didnt

#

its ontop of the fraction

scenic wing
#

now i see

outer kite
#

7/2 root 3

scenic wing
#

they simplified the denom

outer kite
#

yeah ok ChisatoXD

lone heartBOT
#

@scenic wing Has your question been resolved?

lone heartBOT
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queen lion
#

Hey

lone heartBOT
queen lion
#

Just need a quick help

#

How are we able to turn 5 into 1/5 those are not the same in this instance

mortal trellis
#

dividing by 5 is the same as multiplying by 1/5

queen lion
#

Okay nice

#

Does it go other was around too

#

Dividing 5 = multiply 1/5

lone heartBOT
#

@queen lion Has your question been resolved?

mortal trellis
#

dividing 1/5 = multiplying 5

lone heartBOT
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rare bay
#

can anyone help or refer me to where I can learn how to graph/plot simple linear equations on my HP prime G2 calculator?

rare bay
#

there aren't really any good tutorials out there

tardy stag
#

you might just have to explore

lone heartBOT
#

@rare bay Has your question been resolved?

rare bay
#

thanks

lone heartBOT
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grand berry
#

Solo and James are standing at the seashore 35 miles apart. The coastline is a straight line between them. Both can see the same ship in the water. The angle between the coastline and the line between the ship and Solo is 40°. The angle between the coastline and the line between the ship and James is 62°. How far is the ship from Solo?

Here's my take on the problem. Though, I'm not sure if it is correct. Please point out my mistakes if there are any

languid bolt
#

uhh how is the angle in the middle 62 and 40? @grand berry

#

tbh the angles are very wrong

#

the angle that the line from the ship to the coastline makes would sum up to 180 since the coastline is a straight line

#

hello?

#

you here?

languid bolt
#

but the angles you wrote down was wrong

lone heartBOT
#

@grand berry Has your question been resolved?

grand berry
#

My bad

languid bolt
#

are you familiar with the sine formula?

grand berry
#

Yes

languid bolt
#

try using it

grand berry
#

Uhh use it how exactly?

languid bolt
#

are we on the same page here... wait

#

what is the sine formula?

grand berry
#

sinA/a = sinB/b = sinC/c

languid bolt
#

yes

#

you have the angles and you have one of the sides (the coastline)

#

try inserting it into the formula

grand berry
#

Well wouldn't the triangle split into two triangles? I'm just puzzled as to how I should 'insert' it

lone heartBOT
#
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shadow sparrow
#

Not completely sure what I'm missing here... What is f(x)? Its not explicitly shown?

shadow sparrow
#

OH. I'm dumb.

wary stream
#

You're using that to find the area from 5 to 9

shadow sparrow
#

I was looking at the x axis

#

Its asking for what the height is on the y axis

#

šŸ¤¦ā€ā™‚ļø

#

Sorry lol, silly question, thank you for pointing that out

#

.close

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#
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patent swallow
lone heartBOT
patent swallow
#

guys my professor corrected something for me and I've few mistakes, I understand them all except from the integral

#

to start with, why does he write that everywhere?

#

I'm integrating by parts.

#

it's like if idk how to solve a simple integral :/

#

am I missing something

#

no

late token
#

yes

mellow grail
#

for eg. if you have the integral of cos(x) (indefinite)

#

we have sin(x)

#

if you consider the definite integral it must have some bounds

#

say 0 (lower) and pi/2 (upper)

#

we would write it as $\int_{0}^{\frac{\pi}{2}} cos(x) dx$

ocean sealBOT
#

itzkraken.

mellow grail
#

which we can write as

#

$sin(x) |_{0}^{\frac{\pi}{2}}$

ocean sealBOT
#

itzkraken.

mellow grail
#

now you do F(b) - F(a) (a=0, b=pi/2)

mellow grail
lone heartBOT
#

@patent swallow Has your question been resolved?

lone heartBOT
#
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safe tartan
lone heartBOT
safe tartan
#

how would you do this ?

molten pivot
#

Try differentiating under the integral sign

safe tartan
#

i did u substitution of u=y+1 but really didnt do anything

echo socket
#

Geometry or trig sub, which path do you want to go with?

safe tartan
#

umm trig sub because i could do it geometrically

echo socket
#

Then consider either one of y = sin(theta) or y = cos(theta)

safe tartan
#

yep

#

considered

echo socket
#

Well, let us pick y = sin(theta)

safe tartan
#

oh the root3/2 is a giveaway i guess to do trig sub

echo socket
#

thonk No

safe tartan
#

oh is it not

#

cuz like exact value

echo socket
#

The sqrt(1 - y^2) hints at trib sub

safe tartan
#

hmm yea

echo socket
#

$\int_0^{\frac{\pi}3}\sqrt{1 - \sin^2\theta}(\cos\theta\dd\theta)$

ocean sealBOT
#

alonelybean

echo socket
#

Or simply $\int_0^{\frac{\pi}3}\cos^2\theta\dd\theta$

ocean sealBOT
#

alonelybean

echo socket
#

Ever integrated cos^2 before?

safe tartan
#

umm yea

#

what was it again like

#

actually na i dont think i have

echo socket
#

The double angle identity for cosine states that [ \cos2\theta = 2\cos^2\theta - 1]
Rearranging the terms here, we get [ \cos^2\theta = \frac{\cos2\theta + 1}2]

ocean sealBOT
#

alonelybean

safe tartan
#

ah yep i know that one

#

and now cos becomes

#

1/a sin

#

right

#

so here it would be 1/4 sin theta +1/2theta?

#

2theta ofc

#

soz

echo socket
#

Yes

safe tartan
#

thats genius

#

i always struggled with squared ones

#

thanks

safe tartan
#

me rn

#

i got an answer which was 3 solutions but

#

its not an option so

naive crystal
#

Divide both side by 2??

safe tartan
#

maybe i added solutions after multiplying by x somewher

naive crystal
#

,w a^2-2a+2=0

safe tartan
#

oh

echo socket
#

$(2^{\sin^2{x}})^2 \ne 2^{\sin^4{x}}$ btw

ocean sealBOT
#

alonelybean

safe tartan
#

oh yeah oops

echo socket
#

And A^ - 2A + 2 =/= (A - 1)^2

safe tartan
#

yea

#

i still get the same quadratic though

#

for some reason

echo socket
#

Instead it should be (A - 1)^2 = -1, hence no real solutions

safe tartan
#

oh that makes sense

#

quick question, when doing solids of revolution and rotating about the y axis

#

since it becomes pi integral x^2

#

do i just rewrite f(x) in terms of x

echo socket
#

No, it's x^2 dy

safe tartan
#

oh ye

#

so i just write x in terms of y by rearranging

echo socket
#

Yup

safe tartan
#

ive identified it to be B or D, but im not too sure on the bounds

#

do i find the y intercepts of f(x) to find the bounds?

echo socket
#

Should be from y = 0 to y = 0.6pi

safe tartan
#

hmm not sure how you would derive that

echo socket
safe tartan
#

ah i c

echo socket
#

So y goes from 0.6 * 0 to 0.6 * pi

safe tartan
#

thanks

#

for this integral, for what bounds do i integrate the positive case and what bounds do i integrate the negative case?

echo socket
#

You can immedialy rewrite that as 2 times the same integral but going from 0 to 1

#

Because the integrand is an even function

#

Generally $\int_{-a}^af(x)\dd{x} = 2\int_0^af(x)\dd{x}$ if $f$ is even

ocean sealBOT
#

alonelybean

safe tartan
#

yep

echo socket
#

And, |x^2 - 1| = |x - 1| * |x + 1|, but now we are taking 0 < x < 1, so this is equal to (1 - x) * (x + 1)

safe tartan
#

wait no

echo socket
#

x^2 - 1 is negative in this case

#

Either way you look at it

echo socket
#

Yes

safe tartan
#

oh yeah makes sense cuz from 0<x<1 we take the positive case and theres a minus in front

#

is that somewhat right

echo socket
#

Yes, that is right

#

Even if we were not to half the interval

#

We would have -1 < x < 1

#

Meaning 0 <= x^2 < 1 and -1 <= x^2 - 1 < 0

safe tartan
#

mmhm

#

so now im simply integrating -x^2+2

echo socket
#

|x^2 - 1| = 1 - x^2
-|x^2 - 1| = x^2 - 1

safe tartan
#

huh

echo socket
#

|x^2 - 1| = 1 - x^2

So

-|x^2 - 1| + 1 = -(1 - x^2) + 1 = x^2 - 1 + 1 = x^2

safe tartan
#

sorry why does the thing inside the absolute value become switched

echo socket
#

|z| = -z when z is negative

#

We showed that x^2 - 1 is negative

#

Meaning |x^2 - 1| = -(x^2 - 1)

safe tartan
#

oh r u saying that x^2-1 has negative y value for the given bounds

#

that makes sense

#

sorry im quite sloq

echo socket
#

It is fine, take your time

safe tartan
#

yep i got the question, and the answer. Thanks!

#

.close

lone heartBOT
#
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rough sequoia
#

Find the value of
$cos 20 + 2 sin^2 55 - \sqrt 2 sin 65$

ocean sealBOT
#

omniscientzenith

vale wigeon
#

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alpine sable
#

Who turned Ann into an NPC /j

ornate ginkgo
#

That's an mc in disguise of an npc

quiet vector
lone heartBOT
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gilded marten
#

You guys do science physics here?

lone heartBOT
gilded marten
#

I kind of forgot what this formula meant

grim berry
#

but idk maybe

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someone here probably knows

quiet vector
grim berry
#

yep

gilded marten
#

ahh ty ty sorry for the inconvience

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.closew

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.close

lone heartBOT
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steady moon
#

hello, I must find this function's primitive:

steady moon
#

I've done that

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but, why on the answer, they added (1/2)???

gray isle
#

your u' is wrong

#

d/dx of (1+x^2)
isn't x

proven leaf
#

also btw is the primitive just the antiderivative?

steady moon
steady moon
proven leaf
steady moon
#

.close

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zinc lion
#

i have a question abt solving complex fractions

#

(both)

lone heartBOT
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steep marten
#

Hi, could anyone please explain why the bounded area integral trick top function - bottom function doesn't work for this question, and when in general it can be used. Thanks in advance

vale wigeon
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how do you intend to use it

steep marten
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I tried doing integral from 0 to 1(x^r-tangent line)dx but it didn't work

vale wigeon
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well there's a simple reason why it didn't work. you calculated the area of the wrong region!

steep marten
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I know we could do the integral from 0 to 1 (x^r)dx and subtract a triangle area but I am confused as to when the bounded area thing can be used

vale wigeon
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this is the region whose area you calculated.

steep marten
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Oh wait what

vale wigeon
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this is the region bounded by y=x^r and the tangent line between x=0 and x=1.

steep marten
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Okay wait so if I draw a line where the area starts and it hits both curves and then I do it again for where the area ends. If these 2 conditions are met and then I do top - bottom integral it gives me the total area between 2 curves

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Could this be a way to think about it?

vale wigeon
#

nyeh

#

sure

steep marten
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But there has to be a clear top and bottom curve. For example it wouldn't work here because there is no top and bottom curve and the lines at the start and end of the area don't hit both curves?

vale wigeon
#

But there has to be a clear top and bottom curve
yes

steep marten
#

Alright thank you so much Ann I think I understand when I can use it now, when the lines hit both curves and there is a top and bottom curve. Have a great day!

#

Would anyone know how I close this channel?

lone heartBOT
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@steep marten Has your question been resolved?

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gentle shadow
#

can someone explaine this step to me? Idont know where the +4x² at the end come from.

sharp thorn
#

$(2x)^2$

ocean sealBOT
#

bettimsucks

mellow grail
ocean sealBOT
#

itzkraken.

gentle shadow
#

k thx a lot

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@gentle shadow Has your question been resolved?

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mystic comet
#

can anyone confirm if it's -1/2 or 0

lone heartBOT
tardy stag
#

I'm not sure how it could be negative or zero because all of the terms are positive

gray isle
#

as this is a series of positive terms both values are wrong

mystic comet
#

I made it into sum (1/k) - sum (1/(k+1))

tardy stag
#

and what did you get for sum(1/k)?

noble sinew
#

Telescoping series

gray isle
#

what did you do after that

mystic comet
#

1/n which I feel is wrong

mystic comet
#

telescoping

gray isle
#

can you show your work

mystic comet
#

sure

noble sinew
#

Then write it as sum from k=1 to n

mystic comet
noble sinew
#

You only have 2 terms that don’t get cancelled

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Then take limit

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What is $$\sum_{k=1}^5 \frac{1}{k}-\frac{1}{k+1}$$ for example?

ocean sealBOT
#

scapeprof

mystic comet
#

(1/5) -(1/6) ??

gray isle
#

no

noble sinew
#

No

gray isle
#

do you understand summation notation

mystic comet
#

yes i do but it isn't geometric or arithemtic

gray isle
#

can you write what
$$\sum_{k=1}^5 \frac{1}{k}$$
represents, leaving that as a sum, don't bother simplifying

ocean sealBOT
#

ā„amonov

mystic comet
#

1 + (1/2 )+ (1/3) +(1/4) + (1/5)

gray isle
#

yes

#

same question for
$$\sum_{k=1}^5 \frac{1}{k+1}$$

ocean sealBOT
#

ā„amonov

mystic comet
gray isle
#

hence what do you get for:
$$\sum_{k=1}^5 \br{\frac{1}{k} - \frac{1}{k+1}} = \sum_{k=1}^5 \frac{1}{k}- \sum_{k=1}^5 \frac{1}{k+1}$$

ocean sealBOT
#

ā„amonov

mystic comet
#

1+(1/6) ?

gray isle
#

no

#

can you show your work

mystic comet
gray isle
#

for what i was asing for, yes

mystic comet
#

oh

#

1-(1/6) ?

gray isle
#

yes

mystic comet
#

forgot the sign

noble sinew
#

So can you say what $$\sum_{k=1}^n \frac{1}{k}-\frac{1}{k+1}$$ is now?

ocean sealBOT
#

scapeprof

mystic comet
#

1-(1/(n+1))??

noble sinew
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Yes

mystic comet
#

it's the same rule isn't it?

noble sinew
#

Yes

mystic comet
#

i got it thank you

gray isle
#

helps to write out a few terms and align stuff

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$\begin{aligned} 1 &+ \frac12 + \frac13 + \dots + \frac1n \
&- \frac12 - \frac 13 - \dots -\frac1n - \frac{1}{n+1} \end{aligned}$

ocean sealBOT
#

ā„amonov

mystic comet
#

(-1)^n is undefined right?

gray isle
#

there are real value outputs for integer n