#help-39

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pearl pondBOT
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sharp smelt
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still dirge
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Please explain why is the drawing the way it is

lucid anvil
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it might help to understand what the drawing is actually meant to show

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here the drawing is just the region S that you're integrating over

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which corresponds to [0, pi/2]x[0, pi/2]

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the drawing doesn't convey any info about the integrand

still dirge
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Thanks, I do know this.

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I meant this: "it might help to understand what the drawing is actually meant to show
here the drawing is just the region S that you're integrating over
which corresponds to [0, pi/2]x[0, pi/2]
"

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However, what I don't understand is:
why is pi/2 where it is.

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this is not a coordinate system, is it

lucid anvil
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we're just viewing S as a subset of the xy plane

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so like the x coordinate is in [0,pi/2]

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as is the y coordinate

still dirge
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but there's only numbers on xy plane, not angles

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pi/2 is 90*

lucid anvil
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pi/2 is a number

lucid anvil
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it is just a number

still dirge
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okay

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thanks for clarifying

#

.solved

pearl pondBOT
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sharp smelt
pearl pondBOT
sharp smelt
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Hi,how'd I find the mean here? Can I just ingtegrate from theta t infty

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that feels sus

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I'm getting a mean of 1?

past perch
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could you show your work i only managed to simplify and i think youd have to work with limits

sharp smelt
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$\alpha \theta^{\alpha} \int_{\theta}^{\infty} \frac{1}{x^{\alpha}}dx$

past perch
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the mean is xf(x)

sharp smelt
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oh shoot

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I messed uo there

past perch
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yeah you wont get a numeric value i think

jolly parrotBOT
past perch
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yeah now just power rule

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provided a neq 1

sharp smelt
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yea, gives us , uh

past perch
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a > 1

sharp smelt
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$\frac{\alpha \theta^{\alpha}}{(1-\alpha) \theta^{1- \alpha}}$

jolly parrotBOT
past perch
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really? afaik wouldnt we handle the infty lim separately

sharp smelt
past perch
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as x->infty the integral diverges

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oh wait that's for a<1

sharp smelt
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now to find the MLE of mean using invariance

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which is the part I don't gte

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*get

past perch
# jolly parrot **Wai**

wait this isnt checking out can you show the steps cos i think the theta term gets multiplied not divided

sharp smelt
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yes

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so we get $\frac{\alpha \theta}{1- \alpha}$

jolly parrotBOT
past perch
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$\alpha\theta^\alpha \left[\frac{x^{1-\alpha}}{1-\alpha}\right]_{\theta}^{\infty}$

jolly parrotBOT
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sam beam

past perch
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0 -

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so reverses

sharp smelt
past perch
modern talon
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to find the mle of the mean using invariance, you must obtain values alpha hat and theta hat

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i.e find mle's for alpha and theta

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then sub those for alpha and theta in E(X) to find mu hat

sharp smelt
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I thought there's some way without that 😭

modern talon
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unfortunately no

modern talon
# past perch ||i have not done MLE 😭 ||

invariance just means this: if you are trying to find an estimate for some parameter in terms of another parameter with a known MLE, then plugging the MLE into the function produces the MLE of the first parameter

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i.e g(theta) is maximized when inputting theta hat

past perch
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yeah i looked into it it had something with a gamma function(?) i'll check it out after my exams

modern talon
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pareto could be another choice but its a less clean dist than gamma is

sharp smelt
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cool

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thanks

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.close

pearl pondBOT
#
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pearl pondBOT
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torn lodge
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im not too sure how to do part d.
I've found the coordinates for R which was (28cos(theta)/25 , -21sin(theta)/25) and I tried setting the x coordinate to be a variable and the y coordinate to a variable and rearranged both so that i could sub into the identity of sin^2 x + cos^2 x = 1 but i wasnt too sure how that would prove that R has the same eccentricity as the ellipse

torn lodge
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oh and the eccentricity from part a is (root7)/4

heavy onyx
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what equation did u get when u subbed in sin^2(x) + cos^2(x) = 1?

torn lodge
# torn lodge

second fraction is supposed to have 784 on the bottom*

pearl pondBOT
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@torn lodge Has your question been resolved?

torn lodge
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.close

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daring bay
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hello im stuck on the 1.5

pearl pondBOT
rough forge
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Was ist Material 1

daring bay
daring bay
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im about to cry

rough forge
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i dont have tissues but i can try to help

daring bay
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so basically from -1,5 to 1,5 theres one solution?

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i dont understand

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yeah wtf man

steep saddle
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maybe you should integrate it

daring bay
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but what is meant by -1,5 < k < 1,5

honest spear
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i mean you can use symmetry and the fact that the function is strictly increasing after a certain point

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lets call area A(k)

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thing about A(-1.5) compared to A(-0.5)

daring bay
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its not the same

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or wdym

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should i just try integrating it

honest spear
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i mean you can but that defeats the point fr

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cuz then its trivial

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its testing your intuitive understanding

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of the intregral and area

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as k increases

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from -1.5 up until like 1 A(k) is descreasing

daring bay
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yup yeah

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but idk what is meant by solution

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wait

honest spear
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for how many unique k values is A(k)=4

daring bay
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so the area from -1,5 to 1,5

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is 4

honest spear
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no

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wait

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no

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its like 5.something

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you are integrating from k to k+1

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so the width is always 1

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they are just saying there exists

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a k

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between -1.5<k<1.5

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s.t

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A(k)=4

daring bay
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ohhh

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how the hell do you do this with the graph omly

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wtf

honest spear
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do it with the calculus you know

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ig

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then try see how that relates to the graph

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thing is you can see the area is descreasing then increasing

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so it goes less than 4

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then goes back up to 4

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but the function is strictly increasing

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so A(x) is strictly increasing

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A(K)*

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for K>1.5

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so it'll reach 4

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then just keep blowing up

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so theres 1 solution

daring bay
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by reach 4 do u mean reaching like

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4 on the y axis

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wait so you can count area like that?

honest spear
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no like the area is 4

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heres something i threw up

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if you press play on the k value

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it'll show you how the area we are looking at changes as k increases or descreases

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if i were to freeze k at the right moment then A(k)=4

rough forge
honest spear
honest spear
rough forge
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It should just be x=k and x=k+1

daring bay
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but how can you like imagine the area like that

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how can u read the area from the graph

honest spear
honest spear
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under the graph

daring bay
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yo im stupid

rough forge
honest spear
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no

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here me out

daring bay
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wt fman

honest spear
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confirm that yourself

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you know $A(x)=(\frac{x^4}{12}-x^2+4x)_{k}^{k+1}$

jolly parrotBOT
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Nyxzore

honest spear
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thats the integral of f(x)

daring bay
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why /12

honest spear
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4*3 is 12?

daring bay
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oh

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okay

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yeah

daring bay
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so?

honest spear
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now to work out

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this green area you have

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i would need to integrate from -1.5 to 1.5

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notice how thats 2 units long?

daring bay
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yeah

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wdym 2 units

honest spear
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,w 1.5^4/12-1.5^2+4(1.5)-((-1.5)^4/12-(1.5)^2+4*(-1.5))

steep saddle
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isn't that3

honest spear
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yeah

steep saddle
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the answer is 1 k >= 1.5 because its strictly increasing

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see for k = 1.5 A(x) < 4

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since its less than 4 but the function strictly increases and therefore A(x) increases

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there must exist a k such that A(x) = 4

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and there can't be another one for the same reason

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its strictly increasing so A(x) keeps growing to infinity

daring bay
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i just cant seem to understnad what −1,5 ≤ k ≤ 1,5 means

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i cant get it in my head

steep saddle
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it means there is a k in that interval

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such that A(x) = 4

daring bay
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ohhh os

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so

honest spear
daring bay
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from -1,5 to 1,5 theres a starting point a and b for which the area is 4

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basically

honest spear
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well just a

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b can be outside of that interval

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a=k

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b=k+1

daring bay
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but how does that HELP

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for the graph thing

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how did you guys figure it out in your head

honest spear
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This is how

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My function is decreasing starting from -1.5 and i eventually got an area of 4 so i must of started off with an area > 4 then descreased until i got area=4 at k

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but its keeps decreasing so my area gets <4

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but then it starts increasing again

daring bay
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okay so

honest spear
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for k>1.5

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so lets say its stops decraesing at Area=2.71 - made up number

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itll then start increasing again for k>1.5

daring bay
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it stops decreasing at 1,5

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so

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but what does that mean

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wtf

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why is there only 1 solution then

honest spear
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cuz its strictly increasing

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the area starts at some number >4 right?

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lets say 5.7

daring bay
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you mean

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yeah

honest spear
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i go from 5.7 down because my function is decreasing my area must be decreasing

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eventually by area gets to 4

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thats the k they mentioned

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now its keeps decreasing to some number

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lets say 2.71

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and finished decreasing

daring bay
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yes

honest spear
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then my function starts increasing

daring bay
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then it has to increae

honest spear
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at k>1.5

daring bay
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yeah

honest spear
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so my area go up from 2.71

daring bay
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yep

honest spear
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passes 4 again

daring bay
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YES

honest spear
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then blows up to infty

daring bay
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yes this is just logic

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wtf

honest spear
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^

daring bay
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obviously there can only be 1 solution right

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yeah

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i just gotta word it right

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tysm

honest spear
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<#

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❤️

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.done

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!done

pearl pondBOT
#

If you are done with this channel, please mark your problem as solved by typing .close

steep saddle
daring bay
#

.close

pearl pondBOT
#
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pearl pondBOT
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Show your work, and if possible, explain where you are stuck.
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daring bay
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hello, for the 1.2

pearl pondBOT
daring bay
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do i just calculate the inflection point like id do normally?

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because i get f''(x) = 2x

daring bay
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okay but 0 = 2x

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wtf

sweet junco
daring bay
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so x is 0

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yes but

autumn trellis
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What is the issue here?

daring bay
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thats just weird

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it just appears unusual

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and i thought there had to be a catch because it gives 5 full points

sweet junco
daring bay
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why a

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we only need x no??

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i mean the y value

sweet junco
daring bay
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wait

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f(0) = 0

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the fuck

sweet junco
daring bay
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no

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2a

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my bad

autumn trellis
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Any cubic of the form x^3+px+q will have an inflection point at x=0

sweet junco
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yeah

daring bay
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yeah so thats the coordinate?

autumn trellis
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Yes, that's the inflection point.

daring bay
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no way this gives 5 points

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thats 5% wtf

sweet junco
daring bay
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no i think that just translate dpoorly

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let me check the solutions

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yep wtf

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damn

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i thought id have to do some stuff with somelocus

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when is that the case again?

sweet junco
daring bay
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for the exam?

sweet junco
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never seen them used

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ever

pearl pondBOT
#

@daring bay Has your question been resolved?

#
Channel closed

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daring bay
#

so here

pearl pondBOT
daring bay
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can i just say (2k|0) and do 1/2k * x^2 = 0

rough forge
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yes

daring bay
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okay but

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1.2

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do i just calculate the extremes then do the formula for distances

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or

sweet junco
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I think

daring bay
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hmm

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let me think

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yeha if

sweet junco
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k is positive

daring bay
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idk

sweet junco
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so what can we say about the graph

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it's always positive

daring bay
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yeah

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okay

sweet junco
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what are these two points

daring bay
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uhh

sweet junco
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hint, it's when Gk=0

daring bay
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the zeropoints?

sweet junco
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fk(x)=0*

daring bay
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how do you know that

sweet junco
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those are now the minimum values you have so what can you say about the x value of the maximum point of Gk between both minimum points

daring bay
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wait

honest spear
rough forge
sweet junco
sweet junco
sweet junco
daring bay
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yeah but like

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how does that help

silver gulch
sweet junco
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that must mean the x value of the maximum is perfectly in between the x-value of the two minimums

daring bay
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soo

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we do the distance

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from one zeropoint to the other

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?

sweet junco
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we're getting there

daring bay
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okay

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uhh

daring bay
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wait but

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a zeropoint isnt a minimum

sweet junco
smoky gull
sweet junco
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have I been misinterpreting y-intercepts with x-intercepts here

daring bay
sweet junco
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we just established that f(x)__>__0

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so the minimums

daring bay
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okay yes but

sweet junco
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are f(x)=0

daring bay
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okay

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yeah

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i guess

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aso

sweet junco
daring bay
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where were we

daring bay
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maximums

sweet junco
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key word: can

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even if you have f'(x)=0, you can't really tell if they're maximums or minimums from just the slope being 0, you also can't tell if cusps or similar are minimums or maximums

daring bay
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yes but how r u so sure theres minimums at f(x) = 0

rough forge
sweet junco
sweet junco
daring bay
#

ohhhhhh

daring bay
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but

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yea

#

0

sweet junco
daring bay
#

?

rough forge
daring bay
#

roots

rough forge
#

Nullstellen

daring bay
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2

rough forge
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name them

daring bay
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2k and the other one i didnt calculate

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but

rough forge
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u already said it

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0

daring bay
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should i do it rq

rough forge
#

so as nautilus said, f(x)=0 gives you here also the minima which are the "zero points" so at 0 and 2k f attains its minimum

daring bay
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yeah the other one is ß

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0

daring bay
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1/2k * x^2 = 0

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that equals x = 0 right

rough forge
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Yes

daring bay
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ohhh

sweet junco
rough forge
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I would have gone here with the derivative, to conclude that the local max lies on x=||k|| and the prove f is symmetric to x=||k|| in order to conclude same distance from min to max

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by symmetry

daring bay
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how do u even derive that function

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do you need the rule for that

rough forge
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wait i realized you actually need the distance itself

sweet junco
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like

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perfectly in between 0 and 2k

daring bay
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yep yea this makes sense

sweet junco
daring bay
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well

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i mean

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it could be anything

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because of k

sweet junco
daring bay
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1

sweet junco
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now what is 1

daring bay
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the highpoit

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maximum

sweet junco
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1 is k

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don't overthink it

daring bay
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okay

sweet junco
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what is perfectly in between 0 and 2k is (0+2k)/2=k

daring bay
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i mean but

sweet junco
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so we know x=k

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happy 4th of july

rough forge
sweet junco
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oh wait it's may

daring bay
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what

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what did u do there

rough forge
sweet junco
rough forge
#

oh i cant read mb

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i'll leave lmao

daring bay
sweet junco
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nah u stay I gotta sleep

daring bay
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here

sweet junco
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and I fear my explanations would confuse them more

daring bay
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why did you do (0+2k)/2k =k

rough forge
#

Mittelwert

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Both 0 and 2k are equally far away from the maximum, so you just compute the Mittelwert

sweet junco
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except you remove the y value

rough forge
#

(a+b)/2

daring bay
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holy shit

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so you basically sum them up and divide by 2

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is that the distance then too?

rough forge
#

no

daring bay
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thats the x value

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?

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of maxim

rough forge
#

it only tells you at what x the max lies

rough forge
daring bay
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im so smart man

rough forge
#

now you can draw a triangle and use pythagoras

daring bay
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so then y value

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wait so then

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y value of middle value

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and then ^2-^2

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in root

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x, y

rough forge
#

what

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your max lies on (k,f(k))

daring bay
#

like this

rough forge
#

Distance between two points

daring bay
#

yea

rough forge
#

but that's just the same

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it's more intuitive to come up using Pythagoras by urself

daring bay
#

okay but

sweet junco
# daring bay

if you randomly know about arc length formula you can decompose it into this

daring bay
#

i memorized it from vectos

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but

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i can use the (0|0) as one point too?

sweet junco
sweet junco
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that makes it easier

daring bay
#

yeah so

sweet junco
daring bay
#

the problem is

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i think i know how to solve problems, but

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there could so much variation

sweet junco
#

you do not win unless you lose first

daring bay
#

yea but my finals in like 2 days basically

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but ty

sweet junco
#

I've been procrastinating studying multivariate calculus and also forgot the past lessons for the past 12 weeks

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idk tho it is possible ¯_(ツ)_/¯

honest spear
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...?

daring bay
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bro we are fucked 😭

honest spear
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isnt adonis helping

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plus how are you asking more than a question a day 💀

#

1.1 or 1.2

sweet junco
daring bay
#

no i understood it

daring bay
#

people here r really crazy

honest spear
daring bay
#

they help so much

sweet junco
sweet junco
rough forge
sweet junco
daring bay
#

im trying to derive the function

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just for practicing

pearl pondBOT
#

@daring bay Has your question been resolved?

#
Channel closed

Closed by @daring bay

Use .reopen if this was a mistake.

#
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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.
Do not immediately ping people or roles. After 15 minutes, feel free to ping <@&286206848099549185> once.
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Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.

daring bay
pearl pondBOT
daring bay
#

yo so how do i sketch the graph with like 0 info

rough forge
daring bay
#

u mean the z - a part

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?

rough forge
#

yea

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You got pretty much everything in Material 1

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z>a for interval

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then z=a at some point (notice how m behaves there too)

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then a>z

daring bay
#

yeah but how does that help

rough forge
#

draw some lines

#

in the z>a the difference that remains purple, after you subtract the green is what you get for m'

#

Which makes sense in the interval where z>a <=> m'>0 means m is increasing but the slope flattens out as you can see at z=a

#

which means m'=0 so it touches the x-axis

#

then m decrease which means m' will be below x-axis

#

but notice that as m decreases it seems to flatten out again which would imply something like m' -> 0

daring bay
#

yeah i guess but what does that line mean

#

for our m‘

rough forge
#

z-a

#

you are just subtracting function values

daring bay
#

yeah

rough forge
#

if you do some of these you could get a rough idea

#

ig something like

#

,w plot D(x/(x^2+1)) on Plotrange -> {{0, 5}, {-.5, 1}}

#

stupid wolfram

daring bay
#

soo

#

what does the purple line

#

what is it in m'

rough forge
#

the difference

rough forge
#

z distance and a distance now you do z-a, if z is greater then the purple part denotes what's left when we take away the green part (distance of a)

#

Which is the distance from the value of m' at that point

daring bay
#

hmm

#

wait i just realiezd

#

i shouldnt even be doing this exercise

rough forge
pearl pondBOT
#

@daring bay Has your question been resolved?

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haughty cosmos
pearl pondBOT
haughty cosmos
#

I am stuck in last part

#

I found the potential line that is tangent to line and it goes through origin

#

I think I have to find the gradient of line

#

But how do I find the gradient of the line

pearl pondBOT
#

@haughty cosmos Has your question been resolved?

pearl pondBOT
#

@haughty cosmos Has your question been resolved?

dense jasper
# haughty cosmos

tbf if you let $a=|a|e^{i \theta}$, then
$$az^{\ast}+a^{\ast} z=0 \implies x \cos \theta+y \sin \theta=0,$$
which is a line through the origin with normal angle $\theta$. For this line to be tangent to the circle, the perpendicular distance from the centre must equal the radius. This gives you $\cos \theta$, and so $\tan \theta$ immediately follows.

jolly parrotBOT
#

Civil Service Pigeon

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pearl pondBOT
livid goblet
#

<@&268886789983436800>

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junior elm
#

Hello i'm trying to solve this equation and after double checking everything the answers dont match, i dont exactly know what im doing wrong either

livid goblet
#

what was the right answer?

junior elm
#

it said that the answer was 9

torn marsh
#

it's not lol

junior elm
#

no???

dense jasper
#

,w integrate 4x+3x^2 dx from 1 to 2

jolly parrotBOT
dense jasper
#

you can check like this yourself in #bots

junior elm
#

whaat

warped violet
#

By the way

#

The notation is a little funky

#

Writing 2x^2 + x^3 = ... = 13

#

Is incorrect

junior elm
#

are all the answers wrong in my practice sheet then 😭

warped violet
#

Well we can't know that 🙂

junior elm
#

i checked this too

#

i keep getting 5

warped violet
#

Well that is incorrect

livid goblet
#

,w integrate 6x+4x^3 dx from 0 to 1

warped violet
#

Lol

jolly parrotBOT
livid goblet
junior elm
#

it said 4 in the sheet too

junior elm
warped violet
livid goblet
junior elm
junior elm
#

wrong reply oops

livid goblet
#

not 2x^4

junior elm
#

oh

#

oops

#

wait it WOULD be 2x though

#

4/2=2

livid goblet
#

why would it be 2x

#

??

junior elm
#

just like with 6

#

let me show

livid goblet
#

ye but x in 4 is cube

warped violet
#

But again

#

I strongly suggest working on notation

#

This is an integral sign

#

An integral sign from 0 to 1 means nothing

#

Like writing 7x +

junior elm
#

Wouldnt it be that

junior elm
livid goblet
warped violet
#

Either use brackets around [] the expression

#

Or a straight line |

#

But not the integral sign

warped violet
junior elm
#

oh yeah

#

straight line i just noticed

warped violet
#

if we disregard notation again 😭

#

The first integral sign looks like an opening bracket (

junior elm
#

oh NOW i got the answer

warped violet
#

I do suggest working on your notation though. Not just because I like cleanly written math, which I do, but also because it will benefit you. Either on tests (though I don't know how strict your professor is), or on the exit exam (or whatever you have, where it is probably pretty strict)

junior elm
#

yeahh i'll do that

#

just practicing for now

#

i do have another question

warped violet
#

Yeah of course

#

Ask away

junior elm
#

i solved this but i dont understand what happened to the 5 in the middle

warped violet
# livid goblet yes

Though I am going to sleep now, so the person with an extremely long, unique username will probably help you

junior elm
warped violet
#

Best of luck though 🙂

junior elm
#

thanks a lot

livid goblet
warped violet
#

Oof, I fear my life will end before I get to sleep if I do that

junior elm
livid goblet
#

so

#

whats dy/dx of cos(5x)

junior elm
#

minus 5?sinus?

livid goblet
#

?

junior elm
#

i dont exactly know

livid goblet
#

lets say y = cos(u) and u = 5x

#

so that y = cos(5x)

junior elm
#

oooooh

livid goblet
#

taking derivative of y = cos(u) gives dy/du = -sin(u)
derivative of u = 5x give du/dx = 5

#

now to get dy/dx
you multiply dy/du by du/dx

#

du cancels out to give dy/dx
hence dy/dx = 5 × (-sin(5x))

#

this is chain rule

junior elm
#

ooooooh i see

livid goblet
#

basically as you know integration is opposite of differentiation
so you reverse that to find integral of -5sin(5x)

junior elm
#

yeah

#

i think i get it now

#

thank you

livid goblet
#

np

junior elm
#

.close

pearl pondBOT
#
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fading nexus
#

I was able to mostly do these problems but I don’t know I am supposed to know what x and y represent after I find the max or min using my graphing calc

wicked edge
#

For which question, 1 or 2?

merry depot
#

2

wicked edge
fading nexus
wicked edge
jolly parrotBOT
#

Mercury.

wicked edge
#

Then, if you chuck in the calculator, V should be y, and x still be x.

#

It just the change of variable's name.

fading nexus
#

Yea I just don’t understand how I would know on like a test the y value is the volume

wicked edge
#

Depends on what the situation the question is asking about.

merry depot
fading nexus
#

I just don’t know how to figure it out like on a test I would have no idea

wicked edge
fading nexus
#

Wait on the second one I am confused why are we inputting the x value into the r value to find the height

limber nimbus
#

y would be whatever you're finding the min or max of, and x is the value you input to achieve that min or max

fading nexus
#

I put in the height value in for h tho

limber nimbus
#

i dont think there is an x in the second problem

fading nexus
#

So why is the radius the x value

limber nimbus
#

i think it would be good to avoid terminology like "x value" and "y value" tbh

there's different variables here, and some are written to depend on others

fading nexus
#

Like my calc gives the x and y we are finding the volume so the y would be the volume

#

But how would I know the x is the radius

limber nimbus
#

you're basically asking "how do i know if i should solve for V in terms of r or in terms of h before maximizing"

#

the answer is it doesn't matter, either is correct

but one will often be easier than the other

fading nexus
#

I just don’t know how I will solve these problems because without having the answer key I would have no idea what to do next because I would not know the radius is the x value so I would not be able to find the height because I would have nothing to input

limber nimbus
#

again, you don't have to use radius as the x value

fading nexus
#

I’m able to do everything find up until I get the value of the max

fading nexus
limber nimbus
#

im not sure if youre listening to what im saying

fading nexus
#

idk I’m trying I’m just really confused

limber nimbus
#

okay so lets solve using h instead \

we get the same equation of $3 - r^2 = 2rh$ \

rearranging, we get $r^2 + 2rh - 3 = 0$ \

using the quadratic formula, we get $r = h \pm \sqrt{h^2 + 3}$ \

we have to use $r = h + \sqrt{h^2 + 3}$, because $h - \sqrt{h^2 + 3}$ is negative \

so now we can plug in $r = h + \sqrt{h^2 + 3}$ into $V = \pi r^2 h$, and now we have an expression for $V$ in terms of $h$. We can go to our calculator, use $h$ as the x and $V$ as the y, and maximize

jolly parrotBOT
#

snowflake

merry depot
limber nimbus
#

it's more work this way, but it's still a totally valid method

fading nexus
#

I understand that

#

but that’s not the part I’m confused on

wicked edge
# merry depot ty for leaving

<@&268886789983436800> irrelevant information and keep not respecting other helper. I was contributing help and this guy jumped in.

fading nexus
#

like I am a me to do everything I was able to get the max value but I am just not able to identify why the x and y represent

dim linden
limber nimbus
#

there isnt a special unique x for any given problem

fading nexus
#

Yes I know that but I have no idea how to figure out what it represents

limber nimbus
#

what do you mean by represent

fading nexus
#

Like the x represents the radius but I only knew that because I looked at the answer key

limber nimbus
#

because they decided that x should be the radius

fading nexus
#

But there’s a right and wrong answer? How would I know how to continue the problem I alrwdy found the value of height i need to input the radius

limber nimbus
#

they asked for both a height and a radius to maximize the volume

you can either

  1. solve for height in terms of radius and plug in

or 2) solve for radius in terms of height and plug in

if you do 1), you will get a height h and a volume V. then you can solve for r after

if you do 2), you will get a radius r and a volume V. then you can solve for h after

either way, you will get the same exact answers for r, h, and V

fading nexus
#

Like in this problem it turns out both the height and radius equal 1 but not all spinels are like that

limber nimbus
#

thats completely irrelevant

#

once you find radius = 1, you plug that into your equations to solve for height, and then you get that height = 1

fading nexus
#

I’m just very confused

limber nimbus
#

it again seems like you're looking for a unique way to solve the problem, and there isnt one

fading nexus
limber nimbus
#

okay are you saying you dont know how to find the radius after finding the height and volume

fading nexus
#

Like I have (1,pi) but I don’t know how to know that the pi is volume and fhe 1 is the value of the radius

limber nimbus
#

what did you input into your calculator

fading nexus
#

like I am worried on the test I will think the volume is 1 and the radius is pi

fading nexus
#

And then I graphed it and found the maximum volume

limber nimbus
#

okay so you inputted the exact equation you wrote down with V and r, except on your calculator you replaced r with x and V with y

fading nexus
#

Oh wait that kinda makes more sense

#

I never thought about it that way 😭 like it seems obvious now

#

Sorry I feel like I was overthinking it to much

limber nimbus
#

its fine i think just next time be more direct about your question, it was very unclear that you were confused about the actual calculator output

fading nexus
#

Ya sorry my bad

#

I’m stuck on what to do next for this problem

limber nimbus
#

,ccw

#

,rccw

jolly parrotBOT
limber nimbus
#

okay so you have an equation with 1 variable, which means you can solve it for a solution

#

you would use a root finder or equation solver on your calculator

fading nexus
#

should I try to isolate w? That’s the type of thing I did in my previous problems

limber nimbus
#

you could, it's difficult here because you have a cubic equation

#

you could also try expanding everything and factor to find roots, but that can also be difficult with cubics

#

have you seen factoring for cubics and higher in class before?

fading nexus
#

I don’t think so

limber nimbus
#

or factor theorem or anything like that

fading nexus
#

could I find the solution by finding the max or min?

limber nimbus
#

okay then they probably want you to use your calculator to solve this

limber nimbus
#

in the previous examples we had equations with 2 variables, and we wanted to maximize one variable by varying the other one

here we just have 1 variable in the equation, so there's nothing to vary; there's only going to be a few possible solutions, and most likely only 1 valid one

fading nexus
#

I’m just stuck because I don’t really know what u mean by a equation solver

limber nimbus
#

like, (2w + 1)(w)(2/3 w) = 312 is an equation

you can't pick just anything for w, most choices for w would not satisfy this equation

we want to find a w that does satisfy this equation

a simpler version of this is like seeing the equation 3x + 7 = 12, or x(2x + 5) = 13. you have an equation with 1 variable, and you want to solve for what the variable should equal to make the equation true

#

with linear and quadratic equations you can do this directly, but with cubic ones you often will want to use a calculator, unless the equation is easy to factor

#

do you have a ti84?

fading nexus
#

Yes

limber nimbus
#

if you do 2nd trace, then you should see a zero command

fading nexus
#

Is there another way to do this? It’s just our teacher never showed us this before so I’m worried she intends for us to do it a different way

#

Cus she does not like it when people overuse their calculator

limber nimbus
#

mm okay, it's kind of hard if you haven't seen something like factor theorem

#

but maybe you have and just dont recognize the name

#

first, expand the equation so that you have a polynomial that = 0

#

then multiply the equation by constants to get rid of any fractions

#

you then basically just guess roots

#

but if you want rational roots, you only have to check factors of the constant term in the polynomial, divided by factors of the highest-power term

#

once you find one that works, you can factor it out, and you get a smaller polynomial

with cubics, once you find one, you're left with a quadratic, and you can just apply the quadratic formula or try to factor directly

#

this method doesn't work very often though, since lots of polynomials have all irrational roots, so you might not even be able to find that first root

#

here though i checked and there is a rational root so you should be able to find it

fading nexus
#

I looked at the way my teacher did it and for some reason she said find the intersection of the 2w+1 😭

#

So now I’m even more confused

limber nimbus
#

like she wants you to use your calculator?

fading nexus
limber nimbus
#

right okay she does want you to use your calculator

#

intersection and zero do very similar things

#

for intersection, you want to find a w so that the equations

y = 312
and
y = (2w+1)(w)(2/3 w)

intersect. if they intersect, that means that the y-values are the same so 312 = (2w+1)(w)(2/3 w) and you have a valid solution for w

#

zero basically checks for intersections between an equation and the x-axis, so you make one side 0 and plug the other side in

#

both of these commands are in 2nd trace

fading nexus
#

Oh wait we are putting both y=312 and the y = the long one in?

#

That makes more sense

limber nimbus
#

right, intersection needs 2 equations

fading nexus
#

I got confused I thought she meant just out in the 2w+1

#

And I was panicked

#

And when we get the interaction the x value would be the width and the y value would be the volume?

limber nimbus
#

the x value is W and the y value is irrevelant here

fading nexus
#

Ah ok

limber nimbus
#

y is just a dummy variable we use to set the two sides equal

fading nexus
#

And then I would just put in the with into the h equation

limber nimbus
#

youre gonna see y = 312 here because the LHS is just 312

fading nexus
#

What’s LHS?

limber nimbus
#

left hand side

limber nimbus
pearl pondBOT
#

@fading nexus Has your question been resolved?

pearl pondBOT
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turbid lark
#

i understand how to get the theta values. how am i uspposed to get these r values?

#

thx

turbid lark
#

. . .

#

neverm...ind...

#

.close

pearl pondBOT
#
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timber cape
#

oof

pearl pondBOT
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lost fiber
pearl pondBOT
wicked edge
pearl pondBOT
# lost fiber
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
pearl pondBOT
#

@lost fiber Has your question been resolved?

split void
#

as a side note, if you do not find any helper helping after a long time, you may consider posting this is an advanced channel.

#

may be suitable; but I may be wrong; so please find a suitable channel

pearl pondBOT
#
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polar yew
pearl pondBOT
polar yew
#

Could you guys do it on a piece of paper please? I’ve been stuck on this one since yesterday and I’d understand it a lot better visually

light helm
#

did you read what i said yesterday

#

note how you applied power rule to the outer cube
then multiplied by the derivative of the inner (2x+1)
similar idea to what you have here
(sec(x))^3
out is the same, the cube
and inner is the sec(x)
so applying chain rule would result in
3sec^2(x) * d/dx sec(x)
and you can use your table for the derivative of sec(x)

pearl pondBOT
#

@polar yew Has your question been resolved?

pearl pondBOT
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swift spindle
#

Hi is this right

pearl pondBOT
lament dawn
#

i think its right

sweet junco
swift spindle
#

answers do this, so not quite sure

cursive wraith
lament dawn
#

i think

cursive wraith
#

oh wait

swift spindle
lament dawn
cursive wraith
#

yeah they're missing a 2 in the derivative of cos^2(2x)

lament dawn
swift spindle
#

.close

pearl pondBOT
#
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low kestrel
#

hi

pearl pondBOT
wicked edge
#

Hi.

low kestrel
#

are you good with statistics?

wicked edge
#

Any questions?

wicked edge
low kestrel
#

l need some help with trigonometry as well

lament dawn
#

hey, dont ask to ask, just ask!

#

!da2a

pearl pondBOT
#

Asking the actual question right away is more likely to get responses.

Asking "Can I ask...?" or "Does anyone know about...?" doesn't give people enough information to decide whether they can help, and answering can feel like a promise to help with the actual question, which they might find themselves unable to.

low kestrel
#

alright!

wraith jacinth
low kestrel
#

eliminate m from the following equations

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x=1-sinm,y=1+cosm

wicked edge
#

Ask away!

fleet ridge
#

What are you stuck on?

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!status

pearl pondBOT
#
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
low kestrel
#

1

fleet ridge
#

I see

#

Recall that $sin^2x+cos^2x=1$

jolly parrotBOT
#

-TimeLord-

fleet ridge
#

Try using this

lament dawn
#

do you know of an identity involving sine and cosine that does not result in any trigonometric function?

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ah

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well

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that

fleet ridge
#

Oops

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Probably should have waited

sterile python
lament dawn
sterile python
fleet ridge
#

$\sin{x}$

lament dawn
wicked edge
jolly parrotBOT
#

-TimeLord-

fleet ridge
#

Oh snap

lament dawn
fleet ridge
wicked edge
low kestrel
#

prove that (sec x +tan x)(sec x - tan x)= 1 can you also help me prove that equation please?

fleet ridge
#

Did you solve your original problem though?

sterile python
#

wait, stick on each question please.

fleet ridge
sterile python
#

Do not jump from this to other question in a short time!

lament dawn
# low kestrel prove that (sec x +tan x)(sec x - tan x)= 1 can you also help me prove that eq...

what the others said!!

ill assume youre working from first principles since this is another well known pythagorean identity, you can always rewrite, say, trigonometric functions as a ratio of sides, and use the idea that O^2 + A^2 = H^2 and so on

otherwise, you can also derive this from the original pythagorean identity sin^2(x) + cos^2(x) = 1 by rewriting sec(x) and tan(x) in terms of sine and cosine

lament dawn
sterile python
wicked edge
low kestrel
#

thanks so much reze

lament dawn
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no problem!

low kestrel
#

timelord, l didn't solve my first problem though

sterile python
fleet ridge
sterile python
#

Layla blud and that freaky emoji...

lament dawn
low kestrel
#

but y'all been so kind and helpful to me..Thanks a million

proper nova
cinder flower
#

freoji

proper nova
#

ts a help channel 😭

sterile python
low kestrel
#

timelord l already tried mathgpt and discussing with my friends at school

pearl pondBOT
fleet ridge
low kestrel
#

l'll try out that app though

prisma kernel
#

wtb is happening here

low kestrel
#

look it up

pearl pondBOT
cinder flower
#

wtb

lament dawn
#

well, rearrange x = 1 - sin m, y = 1 + cos m in terms of sine and cosine

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i.e.

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make sin m and cos m the subject

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and then employ the identity (holy crap my keyboard is lagging i dont even know how) sin^2 x + cos^2 x = 1

wicked edge
#

Pure chaos here.

lament dawn
lament dawn
sterile python
fleet ridge
low kestrel
#

reze what do i do next?

wicked edge
#

Guys redir

low kestrel
#

l have cosm = y-i,sin m = x+1

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am l on the right direction?

lament dawn
#

right! now you square both sides

fleet ridge
lament dawn
low kestrel
#

wait, is sin m supposed to be x + 1 or x -1

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l feel like l've messed up somewhere

lament dawn
low kestrel
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but sin will be negative right?

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is that ok?

lament dawn
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sin m + x = 1 - sin m + sin m
sin m + x = 1
sin m = 1 - x

cinder flower
#

@lament dawn can i send you a friend request?

low kestrel
#

x = 1-sin m x-1 = -sin m

sterile python
cinder flower
#

no

lament dawn
sterile python
#

🥺

lament dawn
#

LOL

low kestrel
#

thanks

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you're a blessing reze