#help-13

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crisp flint
#

How do i find the least area of line when there's 3 pillars with r = 5 for every pillar and minimum required line width when tying pillars with line

cedar kilnBOT
#

@crisp flint Has your question been resolved?

cedar kilnBOT
#

@crisp flint Has your question been resolved?

subtle harbor
#

!original

cedar kilnBOT
#

Please show the original problem, exactly as it was stated to you, with the entire original context. A picture or screenshot is best. If the original problem is not in English, then post it anyway! The additional context might still be helpful. Do your best to provide a translation.

cedar kilnBOT
#
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raven sandal
#

I have a factor graph and am trying to calculate the probability P(x2=1) with the given probabilities

raven sandal
#

Any help would be greatly appreciated

cedar kilnBOT
#

@raven sandal Has your question been resolved?

raven sandal
#

<@&286206848099549185>

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@raven sandal Has your question been resolved?

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@raven sandal Has your question been resolved?

worn bramble
cedar kilnBOT
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@raven sandal Has your question been resolved?

warped coyote
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wraith daggerBOT
#

Ransik

cloud quartz
#

that’s not a line thats just a point, or its two perpendicular lines

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ah they’re probably referring to the actual lines x = 2 and y = -5, two separate lines

bold hinge
#

Nope

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x=2, y=5 is a line

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r(t) = (2,5,0)+(0,0,1)t

cloud quartz
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Oh woah

bold hinge
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(Position vector) + (direction vector)×(free variable)

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Because z varies freely

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near aurora
#

Cos=-0,8 need to find sin and tg

cedar kilnBOT
subtle harbor
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,tex .unit circle

wraith daggerBOT
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Moosey

silent finch
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Unit circle won’t help

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This just Pythagorean identit

subtle harbor
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ah

#

ye

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$(\cos(\theta))^2+(\sin(\theta))^2=1$

near aurora
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Sin^2=1-0,8^2?

wraith daggerBOT
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Moosey

near aurora
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Sin^2 is 1,64??

subtle harbor
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no...

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cos(theta)=0.8 yes?

near aurora
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-0,8

subtle harbor
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-0.8, alright

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$(\sin(\theta))^2=1-(\cos(\theta))^2$

wraith daggerBOT
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Moosey

subtle harbor
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$\sin(\theta)=\sqrt{1-(\cos(\theta))^2}$

wraith daggerBOT
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Moosey

near aurora
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Will the - change to + ??

subtle harbor
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,calc (-.8)^2

wraith daggerBOT
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Result:

0.64
subtle harbor
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,calc 1-.64

wraith daggerBOT
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Result:

0.36
subtle harbor
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,calc sqrt(.36)

wraith daggerBOT
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Result:

0.6
subtle harbor
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technically, sin(theta) will have two answers since we were squaring before.

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and so tgnt will have two answers

near aurora
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I need the minus one

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For both

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So sin is -0,6?

subtle harbor
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ye :)

near aurora
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What about tg

subtle harbor
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we can verify that sin(theta)=-.6 with Pythagorean identity

subtle harbor
near aurora
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Sin/cos ?

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Would tg be 0.75?

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@subtle harbor

subtle harbor
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,calc (-.6)/(-.8)

wraith daggerBOT
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Result:

0.75
near aurora
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Can you help me with a few more of these so i can get the hang of it

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Ctg is. -sqrt3

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Need to find sin cos tg

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<@&286206848099549185>

subtle harbor
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use pythagorean identity involving ctg

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alternatively draw out the triangle representing ctg. Also you need to specify which of sin and cos are negative

near aurora
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ctg =1/tg?

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is this right?

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ik tg and ctg now how do i find sin and cos

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@subtle harbor

subtle harbor
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$(\cot(\theta))^{2}+1=(\csc(\theta))^{2}$

wraith daggerBOT
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Moosey

subtle harbor
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cot=ctg

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csc=1/sin

near aurora
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i havent lerned thoes ye cot and csc

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so can i use 1+ctg^2=1/sin^2

subtle harbor
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yeah :)

near aurora
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soo sin is 1/2?

subtle harbor
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ye :), or -1/2

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sin and cos have to have opposite sign tho

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since ctg is negative

near aurora
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always?

subtle harbor
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only since ctg is negative

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yea

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if your question mentions something about quadrant that's important to include as well

near aurora
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i need help with one more and thats it

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i need to find cos from

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2tg^2a+3tga+1=0

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@subtle harbor

subtle harbor
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let tga=u

near aurora
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ok

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2U^2?

subtle harbor
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so you get 2u^2+3u+1=0

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apply quadratic formula

near aurora
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ok now what?

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ok wait

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got -1

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and -2/4

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now what

subtle harbor
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now since you know tga=u

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tga=-1 and tga=-1/2

near aurora
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ok so what now?

subtle harbor
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there is another pythagorean trig identity involving tan and sec

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sec=1/cos

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tan=tg

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$(\tan(\theta))^{2}+1=(\sec(\theta))^{2}$

wraith daggerBOT
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Moosey

near aurora
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i havent lernd sec and thoes stuffso is it posseble to do it other way

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tg^2+1 eaquels 1/cos^2

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???

subtle harbor
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you can also draw the right triangle that corresponds to tg=-1 and tg=-1/2

near aurora
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no i need to do it with thes formulas

subtle harbor
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alright, then yeah, use that formula

near aurora
subtle harbor
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solve for cos^2

near aurora
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do i substitute tg?

subtle harbor
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ye

near aurora
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-1 or -2/4

subtle harbor
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both is good, since both are valid for tg

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unless your teacher put any specification

near aurora
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so cos is 1 and 2 is this correct?

cedar kilnBOT
#

@near aurora Has your question been resolved?

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loud stump
#

how do I do this? I've used every standard convergence test I know

raw gulch
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use criterion of cauchy

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$\lim_{n \to \infty } \sqrt[n]{\left| a_{n} \right|}$

wraith daggerBOT
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Joanna Angel

raw gulch
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and then, when you show the convergence of this series, using the theorem on the differentiation of power series, you will calculate the sum of the appropriate power series

loud stump
raw gulch
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yes sure

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look:

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yoru series can be writtien in a scuh form:

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$\sum_{n=0}^{\infty }\frac{\left( -1 \right)^{n}\cdot 3n}{4^{3n}}=3\sum_{n=1}^{\infty }n\left( -\frac{1}{64} \right)^{n}$

wraith daggerBOT
#

Joanna Angel

raw gulch
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do you agree on it ?

loud stump
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yes

raw gulch
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ok to evaluate its sum we have to replace

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-1/64 with x

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and we get power serries of the form:

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$3\sum_{n=1}^{\infty }nx^{n}=S\left( x \right)\text{ }\text{ if}\text{ }\left| x \right|<1$

wraith daggerBOT
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Joanna Angel

raw gulch
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since center of the series is x = 0

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and

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Radius R = 1

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that si easy to find

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so to find oru sum we ned to find S(x)

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we start form geometric series

loud stump
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I see

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got it

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thank you

raw gulch
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$\sum_{n=1}^{\infty }x^{n}=\frac{x}{1-x}\text{ }\text{ if}\text{ }\left| x \right|<1$

wraith daggerBOT
#

Joanna Angel

raw gulch
#

yw )

#

etc

loud stump
#

.close

cedar kilnBOT
#
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undone crystal
#

sorry need help with this again

cedar kilnBOT
undone crystal
#

does anyone here know how to map 3d points onto a plane

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(theyre all coplanar)

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i found the normal vector

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and established 2 perpendicular vectors along the plane

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to serve as x and y

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idk what to do from here tho

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@old ridge

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sorry for ping

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i rlly wanna get this over with tho

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😭

waxen mortar
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Can you be more specific about what you mean by "map" in this case?

undone crystal
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yea

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so i have a bunch of points with x y and z

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they all lie on the same plane

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i want them to only have 2 coordinates

waxen mortar
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Oh, that's a fun thing to do. You've got a few things to do. You've already found the plane in the original coordinate system, but you need another coordinate system to map them into.

Does this plane intersect with the origin of the original space?

undone crystal
#

it can but not necesarily

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im doing this all with variables for a general case

waxen mortar
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If it doesn't, does your use-case allow you to translate the plane and points such that it does?

undone crystal
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use-case?

waxen mortar
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You're asking for a reason, right? (personal interest, a project, a class, ...etc)

undone crystal
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math paper

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my math paper is

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finding the area when a cube is sliced by a plane

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of the polygon formed

waxen mortar
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Oh, neat!

undone crystal
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yea its alot of fun so far

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i assigned the back right corner to be the origin

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so now i have like

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6 points in space

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now i need to map them onto a single plane

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so i can use gauss method

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to find area

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😄

waxen mortar
#

You'll need to decide on an origin for the coordinate system of your plane in some concrete way - could be a point. You'll need to establish basis vectors for your coordinate system - could use two other points on the plane. You may want to correct that to be an orthonormal basis - not too bad hard from there. If you do all of these things, you can probably produce a linear transformation that encodes all of that work.

undone crystal
#

then from there i have my concrete point (r1) and i have 2 perpendicular vectors

waxen mortar
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Sure, just making any one of them the origin is a start.

undone crystal
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i also have the nromal vector

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so i have my plane fully established

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but now how do i make it into x', y' ( ' = new plane)

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rather than x, y, z

waxen mortar
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So think about that point you made the origin. Is there another point on the plane towards which you could draw a vector? If so, normalize that vector. You've got your x' basis. Then, take the cross product of that and your plane's normal. Now, you've got a y' basis.

undone crystal
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i took a random vector between 2 points

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then crossed that with normal

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so i got x' and y'

waxen mortar
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Alright, fair enough. That'll do it. Now that those are real vectors and you have an origin, you need to set up a linear combination of those vectors that reach each other point.

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Those linear combinations will be your coordinates in the plane's coordinate system.

undone crystal
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uh what wopuld that look like

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so like 6 individual vectors?

waxen mortar
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Great question.

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So

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Take the vector from your origin (r1) to some other point (r2)

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That's a perfectly valid vector, right?

undone crystal
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ya

waxen mortar
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Now project it onto x'

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There's the coefficient you get is the x' part of your coordinate.

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Do the same again for y'

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and you have the y' part of your coordinate

undone crystal
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ok

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i think i get that

waxen mortar
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If your x' and y' are normal vectors in the original 3d coordinate system, then your area won't need to be scaled!

undone crystal
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awesome

waxen mortar
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There's also another trick for getting that area, come to think of it...

undone crystal
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im using shoe string method

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but im open to sduggestions

waxen mortar
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That's what I was going to suggest.

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Nice.

undone crystal
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also general question for my paper

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do you think i need to delve into each case

undone crystal
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cus thatll take so long 😭

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i was hoping to make a general formula but i doubt thats possible

waxen mortar
#

That depends on your target audience, honestly.

undone crystal
#

yea your right

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IB is so unclear

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when it comes to ia's

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ok thanks for all the help!!

#

.close

cedar kilnBOT
#
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storm crescent
#

is y=1/2(x+1)^2+5 a vertical compression by a factor of 1/2?

cedar kilnBOT
#

Please don't occupy multiple help channels.

storm crescent
#

.close

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hot rampart
#

How do I find how many sequences of 100 consecutive numbers containing exactly 25 primes?

hot rampart
#

Not sure how to start

amber ridge
#

well, prime numbers are basically random, they don't have a pattern to them

#

are you allowed to write a computer program or smth

hot rampart
#

No you’re not.

potent fractal
hollow minnow
#

Key observation:||for n>11, there are at least 76 numbes in the seqeunce n,n+1,n+2,...,n+99 divisible by 2,3,5,7 or 11 and also note that the sum of 2,3,5,7,11=2310.||

hot rampart
#

This seems quite random…

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How do you prove that?

potent fractal
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You first eliminate all even numbers - there're 50 of them

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Other numbers are of form 2k+1

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They can be ±1, 0 mod 3

hot rampart
#

Oh yeah I see now

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Okay so

potent fractal
#

When k = 1 mod 3 we eliminate the number

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Etc.

hot rampart
#

Okay lemme see

cedar kilnBOT
#

@hot rampart Has your question been resolved?

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urban ermine
#

how do i set this up?

cedar kilnBOT
urban ermine
#

i did $183=0.7x+0.3y$ and $93=0.1x+0.6y$

wraith daggerBOT
#

Joshii

urban ermine
#

and im currently at the matrix $\begin{bmatrix}
0 & 1 & 120\
1 & 6 & 930\
\end{bmatrix}$

wraith daggerBOT
#

Joshii

urban ermine
#

but i dont really understand what this would imply here

cedar kilnBOT
#

@urban ermine Has your question been resolved?

cedar kilnBOT
#

@urban ermine Has your question been resolved?

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split pier
cedar kilnBOT
split pier
#

So my approach in this problem is:
Let c be in R. We construct a sequence x_n of rational numbers in (c, ∞) that converges to c. Then limf(x_n) converge to c² + 1.
Now i construct a sequence y_n of irrational numbers in (c, ∞) that converges to c but then limf(y_n) converge to c. Therefore we get two different sequences in (c, ∞) that converges to different limits by sequential criterion. So right hand limit at c doesn't exist of f(x). Hence second kind discontinuity. Is this right ?

dire geode
#

What does discontinuity of second kind mean

split pier
#

That left hand and/or right hand limit of the function doesn't exist at a point

dire geode
#

Seems fine overall. Maybe you have to cite density of rational and irrational in R

split pier
#

Uhh yeh that's right i think even my prof mentioned it at a slightly similar problem before

#

Thanks for checking

#

.close

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latent totem
cedar kilnBOT
latent totem
#

Anyone?

potent fractal
#

You can use the summation we discussed yesterday

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The one with exponents

latent totem
#

The problem not with the summation

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It's the alpha and beta

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Generalization for the roots

drifting marlin
#

,rcw

wraith daggerBOT
latent totem
#

To find some suitable n for that

potent fractal
#

The sum will be some function g(x)
g(x)=0 has a finite amount of solutions on the specified interval

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Yeah g will depend on n

latent totem
#

I used the sin AP series though

potent fractal
latent totem
#

First I took alpha to be pi/n and 2pi/n as it's standard procedure
Then it didn't work

potent fractal
#

If you want to guess alpha then maybe you should search among alpha such that $e^{i \alpha}, ..., e^{n i \alpha}$ form a regular polygon on the complex plane

wraith daggerBOT
#

EQUENOS

potent fractal
#

2pi/n was a good try but there are also 4pi/n, 6pi/n, etc.

latent totem
#

There would be many though

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And n varies too

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Brute forcing would extend it
I tried with n

vocal crescent
#

One second

potent fractal
#

It's reasonable to calculate the sum

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So we get an explicit expression for g(x)

latent totem
#

The relevant terms of sum are
Sin(nx/2) sin ((n+1)x/2)

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The numerators

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For alpha and beta should satisfy these

royal loom
#

!occupied

cedar kilnBOT
#

Someone else is already using this help channel. If you need help with a question, please open your own help channel/thread (see #❓how-to-get-help for instructions).

latent totem
#

Hey I tried this

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Alpha = a pi/n , beta. = bpi/n

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Got me n = 37.5
Close in our range

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If we do
Alpha = pi/n, beta = 4pi/n
We get n = 15

#

Can we manipulate it in some way to move n closer to our range?
@potent fractal

cedar kilnBOT
#

@latent totem Has your question been resolved?

latent totem
#

.close

cedar kilnBOT
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tawny drum
cedar kilnBOT
tawny drum
#

Does anyone have any resources that can help me train for tests like this

surreal karma
#

Hi! For all?

cedar kilnBOT
#

@tawny drum Has your question been resolved?

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tawny drum
#

hi

cedar kilnBOT
tawny drum
#

scroll up for my question btw

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thin galleon
#

How to approach proving:

cedar kilnBOT
thin galleon
#

$\lim_{n\to\infty}\frac{f(n)}{g(n)}= 0$

wraith daggerBOT
#

kytsu1

astral bay
#

...depends what f and g are

thin galleon
#

🧐

silver fable
thin galleon
silver fable
astral bay
thin galleon
#

The task is to prove

astral bay
#

...where does it say that that's the task

thin galleon
silver fable
astral bay
#

so probably the first step would be to look at the definitions of $\Theta$, $O$, and $\Omega$

wraith daggerBOT
#

bee [it/its]

thin galleon
silver fable
#

ty

cedar kilnBOT
#

@thin galleon Has your question been resolved?

thin galleon
#

O(g(n)) = the output of f(n) is never greater than cg(n)
Θ(g(n)): ~∃ f(n) outside the bounds set by c1g(n), c2g(n)
Ω(g(n)) means f(n) cannot be under the curve of cg(n)

c is a positive constant, n0 is the smallest meaningful value - I don't know why n0 is the smallest value

#

ln x has negative y values when x<1, so perhaps n_0=1 for ln x

#

O(g(n))={f(n) | f(n)∈∫_n0^∞{cg(n)}}

#

I think an analogous problem is to prove that A ⊂ B <=> A ∩ B = A

#

This is fun! 🙂

#

@astral bay do you think this is a good solution?

astral bay
#

...is what a good solution

#

as far as i can tell none of what you've said here is a proof of anything, just restatements of the thing you've been asked to prove

thin galleon
astral bay
#

ok so here's a proof that every number between 0 and 100 is prime

#

is this proof correct?

#

@thin galleon

thin galleon
#

B and C should be prime numbers

astral bay
#

why?

#

the venn diagram shows the proof, x is in A if and only if it is in B and C
i'm doing the exact same thing you did

#

your "proof" doesn't show that B and C are prime numbers

thin galleon
#

This is a good analogy, thank you

astral bay
thin galleon
astral bay
#

yeah i know

#

i'm just giving you a proof that all numbers between 0 and 100 are prime

astral bay
#

the point i'm making here is
a "proof" of a statement isn't just a pile of symbols and various different obviously equivalent formulations of the statement

#

part of the point, the reason that proofs matter at all, is that you can only prove things that are true

#

so if you have a "proof" that works equally well at proving something false, it must not be valid

#

what a correct proof looks like is a series of steps where each step is necessarily true if the previous steps are true

#

producing out of nowhere the claim that $\Theta = O \cap \Omega$ is not a step that immediately and necessarily follows from nothing

wraith daggerBOT
#

bee [it/its]

astral bay
#

if $\Theta$ is the set of primes, $O$ is the set of positive integers, $\Omega$ is the set of integers less than 100, then it's false, for example

wraith daggerBOT
#

bee [it/its]

astral bay
#

and in fact nothing you can do by just symbol manipulation can ever prove that \Theta is the intersection of O and \Omega, because you'd always run into the fact that that's not always true

#

this is why i suggested looking at the definitions - you need to reference the definitions in the proof and deduce things from them

astral bay
#

?

thin galleon
# astral bay ?

I am trying to translate this problem to the prime number example, I find it difficult, but it is interesting. Thank you for the explanations, they make sense.

cedar kilnBOT
#

@thin galleon Has your question been resolved?

cedar kilnBOT
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formal pasture
cedar kilnBOT
formal pasture
#

how do i do 7

#

i dont get how to start it

cedar kilnBOT
#

@formal pasture Has your question been resolved?

formal quest
#

let the circle be a unit circle, which is $x^2+y^2=1$. then how can you express Q's coordinate, using $\theta$?

wraith daggerBOT
#

이재현

cedar kilnBOT
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dreamy totem
#

how is acceleration m/s^2. I understand that it’s messaging the change is meters per second per second, so it would look like 5m/s/1s. However, wouldn’t 1s jump to the top, making it 5m•1s/s canceling out the seconds. Pretty sure the last part is where I’m making a mistake.

crimson delta
#

(m/s)/s is different from m/(s/s)

#

you are thinking of the second

dreamy totem
#

true

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but what is m/(s/s)

crimson delta
#

would just be m

bronze hazel
#

its a sign convention, it means: change of velocity with respect to time
as velocity is written as m/s and time is written as s, change in velocity with respect to time will be m/s per second, which makes it m/s^2

dreamy totem
#

So if a car can go from 0 m/s to 60 m/s west in 1 second then its acceleration would be 60m/s^2?

bronze hazel
#

yes

#

as the change in velocity per second is 60m/s, so acceleration will be 60m/s^2

dreamy totem
#

okay thank you

bronze hazel
#

welcome

crimson delta
#

well, average acceleration over that second. probably not the same during the whole second

dreamy totem
#

isn’t the average acceleration always different in between the start and end time

#

Also how can you find instantaneous velocity, position, and acceleration using algebra I thought that required calculus

#

@crimson delta

crimson delta
#

yes that usually requires calculus

#

except for some very simple cases I guess

dreamy totem
#

ok thanks

#

.close

cedar kilnBOT
#
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latent totem
cedar kilnBOT
latent totem
#

.rotate

#

help please

#

?

wraith daggerBOT
cedar kilnBOT
#

@latent totem Has your question been resolved?

latent totem
#

.close

cedar kilnBOT
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true galleon
cedar kilnBOT
true galleon
#

How would you solve this?

inland sky
#

first: there's a common factor in every term. what is it?

true galleon
#

X

inland sky
#

Ok, so that's factored out

true galleon
#

We can pull x out

inland sky
#

now we have x(x^3 + x^2 + 4x + 4)

#

Now: attempt to factor out something from x^3 + x^2 and 4x + 4 separately

true galleon
#

From x^3 and x^2 we can factor out x^2

inland sky
#

ok so we have x^2(x+1) and then for 4x+4?

true galleon
#

4

inland sky
#

and the other factor?

#

4 times

true galleon
#

But wait, what happens to the x we factored out beforehand too?

true galleon
inland sky
#

no, 4*x + 4 does not equal 4 times 2

true galleon
#

Oh hang on…

#

4(x+1)?

inland sky
#

Yes, so now we have x^2*(x+1) + 4(x+1)

#

do you see what we do next?

true galleon
#

(x^2 + 4) (x+1)?

inland sky
#

Yep, now you're done

#

so the final answer is x(x+1)(x^2+4)

true galleon
#

Thank you!!!!

#

.close

cedar kilnBOT
#
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inland sky
cedar kilnBOT
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weak ore
#

how is −4(1+k)(9) = -36-36k and not just 36k?

jade charm
#

Multiply

weak ore
#

my logic is that -4*(1+k) = -4k

jade charm
#

That is false

weak ore
#

and -4k*9=-36k

jade charm
#

You need to distribute

weak ore
#

okayy yeah i get it now

jade charm
#

If you're ever unsure about that sort of stuff, try plugging in a concrete value of k

#

For instance k=-1

weak ore
#

yeah thanks

#

,close

#

.close

cedar kilnBOT
#
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cedar kilnBOT
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formal pasture
cedar kilnBOT
formal pasture
#

how did they get cos2x at end agaib

#

again

glacial heron
#

can you show the whole image

#

what was the question?

formal pasture
glacial heron
#

so sin4x

formal pasture
#

yes

#

i got the first setp

#

but when they factored 2 out

#

i got lost

crimson sedge
#

hey,, can i get some help w math?..

glacial heron
#

2 * sin2x * cos2x?

formal pasture
#

wouldnt it be 2(sinxcosx)

glacial heron
#

no

formal pasture
#

hm

glacial heron
#

we can so a substitution method at first to make it easier to understand

#

let’s say u = 2x

formal pasture
#

okay

glacial heron
#

you then have sin(2u)

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then use the double angle formula

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and you get 2 * sinu * cosu

formal pasture
#

yes

glacial heron
#

replace u with 2x

formal pasture
#

wdym again

glacial heron
#

2 * sin2x * cos2x

#

mb

formal pasture
#

4x?

glacial heron
#

?

formal pasture
#

isnt that

#

sin4x

glacial heron
#

yes

formal pasture
#

okay

#

so what is next

#

i get those steps

glacial heron
#

just do the double angle formula again

#

for both sin2x and cos2x

formal pasture
#

how did they get (2)(2sinxcosx)(cos2x)

glacial heron
#

sin2x = 2sinxcosx

formal pasture
#

i dont get where thr last came from

formal pasture
glacial heron
#

so 2(sin2x)(cos2x) becomes 2(2sinxcosx)(cos2x)

formal pasture
#

why didnt cos2x

#

become smthn else

glacial heron
#

they were probably focusing on sin2x first

formal pasture
#

ok

#

yo but how did 2sin2xcos2x

formal pasture
#

that

#

like they just subbed in

#

the doublr angle

glacial heron
#

yes

formal pasture
#

formulas?

#

ou

glacial heron
#

yup

#

that’s all

#

it’s still mathematically correct

formal pasture
#

bruh they couldve just said that

#

sob

glacial heron
#

oh well, now you know

formal pasture
#

okk tysm

#

:DD

#

.close

cedar kilnBOT
#
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manic cipher
#

Goooodddd afternoon

cedar kilnBOT
manic cipher
#

I'm solving a question in logarithms that says i need to find the domain for f(x)=ln x^2-x-6. While solving, i ended up with the answer (-oo, -3)U(2, oo) as i used (x-3)(x+2) when factoring the problem. However, when using mathway to confirm my answer, it gives me (-oo, -2)U(3, oo)

#

I was wondering if the reversal of my answer actually matters or if there's something i'm doing wrong

#

When factoring x^2-x-6, -3 and 2 both multiply to -6 and add to -1, so i'd assume my answer was correct. But if the true answer is what math way gave me, what am i doing wrong?

#

here's the photo of the question

glacial heron
#

the domain for a polynomial is all real numbers

#

ah

manic cipher
#

I forgot to put ln my apologies

glacial heron
#

since the polynomial's domain is all real numbers, you just have to worry about the domain for the natural log function

manic cipher
#

what do you mean?

mortal hemlock
#

for what values is $ln(x)$ defined

wraith daggerBOT
#

Flappie

manic cipher
#

what do you mean defined?

#

i'm sorry if i'm a little slow, it's been hard trying to understand this

mortal hemlock
#

what is $ln(-1)$?

wraith daggerBOT
#

Flappie

manic cipher
#

-4? -1^2 is 1, so 1+1= 2 and 2-6= -4

#

so ln(-1)= -4

mortal hemlock
#

ln(-1) actually is not defined

manic cipher
#

Ohhhhh i see my mistake there

glacial heron
#

basically negative numbers

#

and 0

manic cipher
#

I mixed up ln with f(x)

#

okay so ln(-1) isn't defined

mortal hemlock
#

yes, and for what other values for x is ln(x) not defined

manic cipher
#

0?

glacial heron
#

that's one value, yeah

mortal hemlock
#

0 is one of them yes, but which other ones

manic cipher
#

Any negative value im assuming?

mortal hemlock
#

yes

manic cipher
#

Any value less than 0?

#

Ah okay

mortal hemlock
#

for any x<=0 ln(x) is not defined

manic cipher
#

Okay got that

mortal hemlock
#

what does this mean for the domain of ln(x)

manic cipher
#

I don't know

mortal hemlock
#

do you know what the domain is

#

just the term

manic cipher
#

wait the domain for ln(x)?

#

is that what you mean by the term?

mortal hemlock
#

if i say the domain of some function f(x), what do i mean by that

manic cipher
#

All i know is that the domain is the x's

mortal hemlock
#

but if x<=0

#

we concluded a moment ago that ln(x) is not defined for those x's

#

so would those x's be in the domain?

manic cipher
#

No?

mortal hemlock
#

correct

#

so then what is the domain of ln(x)

#

if x<=0 is not in it

manic cipher
#

(0, oo)?

glacial heron
#

bingo

mortal hemlock
#

indeed

#

basically, any positive number

manic cipher
#

Ah okay now i understand that

#

Okay

mortal hemlock
#

so then what if we have ln(x-3)

#

hwo does this change the domain

manic cipher
#

well then it'd be 3 and any positive number above it right?

#

(3, oo)?

mortal hemlock
mortal hemlock
manic cipher
mortal hemlock
#

then what if we have ln(g(x))

#

what does g(x) need to be for this to be defined

manic cipher
#

I'm using parenthesis so i'm assuming not

manic cipher
mortal hemlock
mortal hemlock
#

so now what if we look at the original question

#

what does that ask

manic cipher
#

it asks for the domain of f

mortal hemlock
#

if we look at the function

#

what is f(x)

manic cipher
#

and f(x)= ln x^2-x-6

mortal hemlock
#

*with an ln

manic cipher
#

Right sorry

mortal hemlock
#

so with what we have concluded earlier

#

what is in the case the g(x)?

manic cipher
#

I don't know

mortal hemlock
manic cipher
#

Oh right greater than 0

mortal hemlock
#

exactly

#

so then what about ln(x^2-x-6)

#

what needs to be greater than 0

#

for this function to be defined

manic cipher
#

x?

mortal hemlock
#

not quite

#

if x=-10

#

then ln(x^2-x-6)=ln(100+10+6)=ln(116)

#

so this is defined

manic cipher
#

That's because 116 is a positive number

glacial heron
#

hint hint interval test

manic cipher
#

if the number is negative, it would be false, if it was positive, it'd be true

mortal hemlock
#

how would you check if its positive or negative

manic cipher
#

Well, i know that in the number line after i factor x^2-x-6, i pick any number in each section (in beween -oo and -3, -3 and 2, etc.) so i would replace x with that number and solve the problem

#

then the answer i get should be either negative or positive

#

that's how i learned it

mortal hemlock
#

x^2-x-6 = (x-3)(x+2), right?

manic cipher
#

Yes

mortal hemlock
#

so, ln(x^2-x-6)=ln((x-3)(x+2)), right?

manic cipher
#

Yes

mortal hemlock
#

and we need this function to be defined, so whatever is inside the brackets of the ln needs to be greater than 0

manic cipher
#

Are you saying that whatever is in the domain has to be greater than 0? Is that what you mean by inside the brackets?

mortal hemlock
#

ln(stuff inside the brackets)

manic cipher
#

OH okay

mortal hemlock
#

this is what i mean by 'stuff inside the brackets'

#

x^2-x-6 is a parabola and by factoring it, we can easily see what the intersections with the x-axis are

manic cipher
#

Okay yeah i get that now

#

Okay

mortal hemlock
#

(x-3)(x+2) is that factorization, so what are the intersections?

manic cipher
#

-3 and 2?

mortal hemlock
#

close

manic cipher
#

wait

#

3 and -2?

mortal hemlock
#

yes

#

you can see it as x-3=0 or x+2=0

manic cipher
#

Yup

mortal hemlock
#

so if we take the point x=3

#

if we go up, does it go positive or negative

#

if we go down, does it go positive or negative

#

same for x=-2

manic cipher
#

Well, for -2 if it were to go up it would become positive right?

mortal hemlock
#

so, if i fill in x=-1 it will be a higher value then when i put in x=-2?

#

Might be easier to graph it so you can visualise it

manic cipher
#

Oh wait. If i'm replacing the x's with -1, the answer would come out to be -4. But if i replaced with -2, the answer would be 6.

#

So if we go up, it will become negative

manic cipher
mortal hemlock
#

this is what you get

manic cipher
#

I still haven't come to understand how the answer would be (-oo,-2)U(3, oo) and not (-oo, -3)U(2, oo). But i think im getting somewhere

#

Ah okay

mortal hemlock
#

we can see our points x=3 and x=-2

#

from (x-3)(x+2)

manic cipher
#

Okay

mortal hemlock
#

in this graph, for what intervals is this function positive

manic cipher
#

(0, oo) i'm guessing

#

cause anything below that is negative

mortal hemlock
#

for what values of x, do we get a positive value for y

manic cipher
#

Oh 3 and anything above

mortal hemlock
#

maybe phrased like this its better

#

yes, (3,$\infty$)

wraith daggerBOT
#

Flappie

mortal hemlock
#

and what else?

manic cipher
#

and -2 and anything below

mortal hemlock
#

exactly

#

so we have the two intervals (-inf,-2) and (3,inf)

#

for which our function x^2-x-6 is positive

#

together with our knowledge of the domain of ln(g(x))

#

we know that ln(g(x)) is defined for g(x)>0

#

in our question, g(x)=x^2-x-6

#

with all of this combined

#

what is the domain of ln(x^2-x-6)

manic cipher
#

(-oo, -2)U(3, oo)

mortal hemlock
#

boom

manic cipher
#

OHHHHHH

#

I get it now

mortal hemlock
#

thats fantastic

#

do you also know why?

manic cipher
#

Why what?

mortal hemlock
#

why this is the solution

manic cipher
#

😅

mortal hemlock
#

if i gave you ln(x^2-5x+6) would you be able to give the domain aswell?

manic cipher
#

Probably yeah

#

I could give it a try

#

give me a min

mortal hemlock
#

or ln(x^2+3)

#

you can also just write your thought process here

manic cipher
#

Okay so i factored the first one you gave me. I factored it into (x-2)(x-3)>0

mortal hemlock
#
  • =0, but yes
manic cipher
#

Oh in a video i watched they just put >

#

But = yeah that's what i mean

mortal hemlock
#

actually, that also works

#

mb

manic cipher
#

For the numbers in between and above/below, i chose -4, -2.5, and -1

#

since -2 and -3 are right next to each other, could either or just be used instead of a decimal?

#

like just use -2 instead of -2.5?

mortal hemlock
#

at -2 and -3 its 0

#

so it wouldnt give you much information

manic cipher
#

Oh okay

mortal hemlock
#

what you could do, is take the derivate and evaluate them at x=-2 and x=-3

manic cipher
#

After replacing x with -4 i got 42

mortal hemlock
#

42?

#

oh right, mb

#

ignore that

#

:)

manic cipher
#

Haha okay

mortal hemlock
#

so 42 is positive

#

and -2.5 and -1?

manic cipher
#

solving that now

mortal hemlock
#

oh wait

manic cipher
#

?

mortal hemlock
#

are you sure its at x=-2 and x=-3?

#

i see why i was confused now

manic cipher
#

well yeah, -2 + -3 = -5 and multiples it gives 6

mortal hemlock
#

if i fill in -2 at (x-2)(x-3)

#

i get (-2-2)(-2-3)=-4*-5=20

#

thats not 0

manic cipher
#

okay wait now i'm confused

mortal hemlock
#

but -2 and -3 are not the roots

#

(roots are where the fucntion is 0)

#

the roots are x=2 and x=3

manic cipher
#

What?

#

Oh

#

Ohhh

#

Okay

mortal hemlock
#

because (2-2)(2-3)=0*-1=0 and (3-2)(3-3)=1*0=0

manic cipher
#

Okay okay

#

This is so much to think about...

mortal hemlock
#

it'll be muscle memory once youre used to it

manic cipher
#

I hope so

mortal hemlock
#

so back to ln(x^2-5x+6)

#

what is the domain

manic cipher
#

Wait before i get the domain, do i need to change the sign of the numbers in the line? Cause i used -2 and -3 originally so i should change that to positive numbers?

mortal hemlock
#

you want the roots

#

which are 2 and 3

#

so, yes? if trhats what youre asking

manic cipher
#

Oh okay

#

Is it (2,3)U(3, oo)??

mortal hemlock
#

almost

#

is (2,3) the correct interval?

#

if necessary, look at its graph again

manic cipher
#

(-oo, 2)?

mortal hemlock
#

yes

#

so its domain is (-inf,2)U(3,inf)

#

correct?

manic cipher
#

Yeah

mortal hemlock
#

so now what about f(x)=ln(x^2+3)

#

what is its domain

manic cipher
#

Would the factor for x^2+3 be (x-3)(x+3)?

mortal hemlock
#

no

#

if you work out those brackets you get x^2-9

#

dont try to factor this one

manic cipher
#

Oh

mortal hemlock
#

you can see at a glance

manic cipher
#

Okay

mortal hemlock
#

when is this function positive

manic cipher
#

I dont know

#

Is it positive at 3?

mortal hemlock
#

is x^2 ever negative?

manic cipher
#

No

mortal hemlock
#

so is x^2+3 ever negative?

manic cipher
#

No

mortal hemlock
#

so where is ln(x^2+3) defined?

manic cipher
#

any number greater than 0?

#

x>0

mortal hemlock
#

we just concluded that x^2+3 is never negative

manic cipher
#

So it's never undefined?

mortal hemlock
#

exactly

manic cipher
#

So if it's never undefined

mortal hemlock
#

the whole domain is just R

manic cipher
#

Would the domain just be -oo, oo?

mortal hemlock
#

yep

#

thats R

manic cipher
#

Oh okay

mortal hemlock
#

idk how to do the latex cool R thing

#

one sec

granite knoll
mortal hemlock
#

$\mathbb{R}$

wraith daggerBOT
#

Flappie

mortal hemlock
#

here

mortal hemlock
manic cipher
#

Oh

mortal hemlock
#

idk if you've had those numbers

#

anyway

#

idk if i explained it properly

#

the whole thing

#

im new to this

manic cipher
#

It's a bit difficult to understand but it's not your fault. I'm a little bit tired and have been studying for a while trying to master logarithms

mortal hemlock
#

were the small steps useful or annoying

manic cipher
#

Domain of logarithms is what i'm just having most trouble with

#

They were useful

mortal hemlock
#

glad to hear

manic cipher
#

I was able to identify some mistakes i've made

#

I'll just need to practice more. Thank you though for the help i really appreciate it

mortal hemlock
#

no problem

#

if your question is solved you can close the channel

manic cipher
#

Actually, if you don't mind, would it be okay if i can dm you if i need help with anything else? Despite my misunderstandings, you were really helpful and i'd like to learn a bit from you

mortal hemlock
#

yes sure, i dont mind

manic cipher
#

Oh cool thanks! I really appreciate it

#

.close

cedar kilnBOT
#
Channel closed

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#
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After 15 minutes, feel free to ping <@&286206848099549185>.
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modest shadow
cedar kilnBOT
modest shadow
#

how do i grpah this without a calculator

cedar kilnBOT
#

@modest shadow Has your question been resolved?

modest shadow
#

<@&286206848099549185>

nimble veldt
#

It depends on how accurate the graph needs to be.

modest shadow
#

oh

#

well its like this

nimble veldt
#

well then just think how the function behaves. eg. if x grows -> 0.2/x goes to 0 -> e^(0.2/x) goes to 1 and f(x) goes to 2. and so on. what happens if x goes to 0 from the left, then from the right, ...

modest shadow
#

what abt the asymptotes

nimble veldt
#

i am not sure what you mean. what should be about asymptotes?

modest shadow
#

like how to find them

#

wihtout a calculator

nimble veldt
#

just as i said before: think how the function behaves. e.g. what happens to the graph if x grows?

#

what is with x = 1000, x = 10000, x = 100000, ...

modest shadow
#

oh ok

#

thanks .close

cedar kilnBOT
#

@modest shadow Has your question been resolved?

modest shadow
#

didnt close it right 💀

cedar kilnBOT
#
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#
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Ask your math question in a clear, concise manner.
Show your work, and if possible, explain where you are stuck.
After 15 minutes, feel free to ping <@&286206848099549185>.
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• Be polite and have a nice day!

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empty berry
#

Hi

cedar kilnBOT
crimson sedge
#

hi

empty berry
#

How r u

upper garnet
#

Good and u?

empty berry
#

Can anyone here teaches me grade 9 math

crimson sedge
#

probably

empty berry
royal loom
#

If you have a specific question you need help with, ask it

#

Otherwise the point of these channels are not to teach you entire subjects

empty berry
#

Im not getting even a single thing

crimson sedge
#

about what

empty berry
#

yeah right

#

so let me give you question

empty berry
velvet hemlock
#

ask ur question

empty berry
velvet hemlock
#

are you familiar with laws of power?

hollow minnow
#

,,\expolaws

empty berry
wraith daggerBOT
velvet hemlock
#

Ty pure

#

ye read it i guess

empty berry
royal loom
#

So where are you stuck?

empty berry
#

ok

velvet hemlock
#

maybe in (ii) u can use the fact that:
(x-a)(x+a) = x^2 - a^2

empty berry
#

I just dont know how to solve or go further like where to start

velvet hemlock
#

if ur not familiar with

#

lets start with (i):
u agree that 120/30 = 4?

empty berry
#

yeah

velvet hemlock
#

aight you agree that x^2/x^3 = x^-1?

#

which is also eqaul to 1/x

empty berry
#

yes

velvet hemlock
#

aight u agree that y^3/y = y^2?

empty berry
velvet hemlock
#

y^3 / y = y^3/y^1 = y^3-1 = y^2

#

Quotient of power

velvet hemlock
empty berry
#

oh ok

velvet hemlock
#

can u try now to complete it?

empty berry
#

ok

velvet hemlock
#

u can tag me if u need help with others

empty berry
#

is it 4x^-2y^2z^3

#

Is my answer correct @velvet hemlock

velvet hemlock
#

u sure x^-2?

empty berry
#

oh it should be 1 / x^2

#

but how will it fit in equation

#

Ok its 2:24AM

#

Gn

#

see ya'll later

#

It would be nice @velvet hemlock if you finish answering me

velvet hemlock
#

its x^-1

#

not x^-2

empty berry
#

oh

#

yeah my mind

#

ok Thanks

#

see ya later

#

bye

#

Gn

cedar kilnBOT
#

@empty berry Has your question been resolved?

cedar kilnBOT
#
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cedar kilnBOT
#
Available help channel!

Send your question here to claim the channel.

Remember:
Ask your math question in a clear, concise manner.
Show your work, and if possible, explain where you are stuck.
After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!

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graceful rose
#

Suppose Lisa has a collection of 20 necklaces. Twelve are made of pearls, 6 are made of gold, and 2 are made of both pearls and gold. If she randomly selects 5 necklaces to wear to a gala event, find each probability.

P(2 pearls and 3 gold or 1 pearl and 4 gold)
P(at least 1 necklace made of pearls or gold, but not both)

cedar kilnBOT
#

@graceful rose Has your question been resolved?

#
What step are you on?
1. I don't know where to begin.
2. I have begun but got stuck midway.
3. I got an answer but I was told that it's wrong.
4. I got an answer and would like my work checked.
5. I have a question about someone else's work/solution.
6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
#
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#
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Remember:
Ask your math question in a clear, concise manner.
Show your work, and if possible, explain where you are stuck.
After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!

Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.

reef hare
#

For this question, I think I got a) and b), in the sense that a) is just P(AandB) = P(A)P(B), and b) is just when they are mutually exclusive P(AandB) = 0 so it's minimu, but what's the condition for the maximum?

cerulean sail
#

Hint: if both A and B have happened, then A has to have happened, and B has to have happened...

cedar kilnBOT
#

@reef hare Has your question been resolved?

cerulean sail
#

Not quite SCNOOOO

#

You have to have A happen (which has probability 0.3) and you have to have B happen (which has probability 0.8) for A and B to happen both

reef hare
#

So that's the same as a)? assuming that they're indepdent and just using the multiplication rule

cerulean sail
#

Not quite either SCNOOOO

reef hare
#

😭

cerulean sail
#

It's not that they're independent that you want to look for, but rather, something else (not mutually exclusive either)

reef hare
#

Ohhhhh

#

B is dependent on A?

#

or something like that

#

Actually A is dependent on B

#

like if B happens A is guaranteed to happen

#

or something like that

#

Those cat emojis are so cute

cerulean sail
#

I love the cat emotes catlove

reef hare
#

So practically P(AnB) = P(B) because if B happens A is guaranteed to happen, as such P(AnB) = 0.8

cerulean sail
#

But for example, it's more likely I'm typing this in bed than it is that I'm typing this in bed and drinking hot chocolate, that's the idea

cerulean sail
reef hare
#

Wat

#

Wait

#

I'm

cerulean sail
#

Note that P(B) is bigger than P(A)

reef hare
#

Given that P(B) has happened...