#help-49

1 messages · Page 126 of 1

obtuse totem
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but then the inner circle part would be principal

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oh

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wait what

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no this doesn’t make sense

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the first shows |z-4|<4

radiant roost
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0<|z-4| simply excludes the point at 4

obtuse totem
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so i don’t have to find a series for it?

radiant roost
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i don't know about laurent series

obtuse totem
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because in these examples, the graph is always split into two or three

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note the eg for 3) is not done, I can show the rest tho

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yea i’m not sure how to solve this

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<@&286206848099549185>

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cause you cant change it to a geometric series if its not a simple pole right?

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omg i cant even watch youtube videos im pretty sure you cant just have a constant here

radiant roost
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hm? looks like a partial fraction decomposition

obtuse totem
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oh yes

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thats my bad im remembering smth wrong

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its only if you expand it out that you have to do bx+c

radiant roost
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ah

obtuse totem
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or like in form (x+b)^2

radiant roost
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i think there's a special rule in that case

obtuse totem
radiant roost
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do i understand example (1) correctly?
when |z|<2, the principal part of the laurent series is 0
when |z|>2, the analytic part is 0

obtuse totem
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also I think you can split into two parts you have 0<|z-4| which is principal part and |z-4|<4 which is analytic

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but Im not sure if you can change into geometric series cause one of the poles is power 3

radiant roost
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but for |z|<2, you've written f as a series with z^n, which should comprise the analytic part, no?

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and that series is meant to be the laurent series?

obtuse totem
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@tribal temple hii

obtuse totem
radiant roost
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in general, yes

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hello charbit

radiant roost
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so for example (3), when 1<|z|<2, do you have f as the sum of 2 series?

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or is it still just 1 series like the other examples on that page

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i imagine it will have 2: one for the analytic part and one for the principal part

obtuse totem
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oh it seems like you only need to find expansion when z=0

obtuse totem
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because

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in this example, since the singularities 1 are inside the area i guess it doesnt have to be expanded? not sure why tho

radiant roost
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(z+1)/(z(z-4)^3) is undefined when z=0
how can you find an expansion when z=0?

obtuse totem
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sorry worded it wrong, 0<|z-4|

radiant roost
obtuse totem
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oh derivative!

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oh

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wait

radiant roost
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??

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it seems example (3) also makes use of partial fraction decomposition

obtuse totem
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I'll send a photo soon dw

radiant roost
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all right

radiant roost
obtuse totem
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no im stupid its the same thing as eg3. both annulus

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just wait ill send a photo

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yup

radiant roost
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yes but presumably eg3 solves it for different domains

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0<|z-4|<4 is an "annulus" but the central hole is only a single point

obtuse totem
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@tribal temple can you explain how to do this question

obtuse totem
tribal temple
obtuse totem
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ok, thank you!

radiant roost
midnight plankBOT
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midnight plankBOT
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@obtuse totem Has your question been resolved?

midnight plankBOT
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@obtuse totem Has your question been resolved?

obtuse totem
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ok idk if ill be back in a while

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we'll see

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deft quarry
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I have like 3 sources telling me what to do in very different ways, and now I'm confused. Should I do the derivative first thing on the equation, or? @~@ And if so, should you not go past the point they did in the 2nd pic? I originally did and got -12x-8x^2+6x^3+9, but that was wrong according to another calculator T~T

warm vine
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Are you the kind of person who tries to avoid the product rule?

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As is often the case with math, there are a couple ways to solve it

deft quarry
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I do try to avoid it, but failed here xD

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that's where I got the -12x thingy from

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Ig I could just stop at where they stopped, and do the whole plugin thingy 🤔

warm vine
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Is there a way you can rewrite f(x) to avoid having to use the product rule?

deft quarry
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I'm guessing f(1) is not the answer

warm vine
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Although I think the derivative you found using the product rule looks correct, so you could just use that

deft quarry
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:D yay

warm vine
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What does the derivative mean?

deft quarry
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slope of the tangent line

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ah oki so that's where the point slope comes in

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I seeee

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ok I might've been overthinking this xD

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justpossibly

warm vine
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That’s easy to do with math

deft quarry
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I'm good with manipulating point slope and slope int, I can do the rest of this, thank you :D

warm vine
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You’re welcome

deft quarry
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I was very unsure about the derivative's correct-ness, ty for checking it :')

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have a good afternoon :)

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umbral cave
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When determining sequence convergence or divergence and I have (-1)^ncos(npi) can I just bound cos and then dct it with something that has one as a placeholder for it?

midnight plankBOT
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deft quarry
robust isle
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you can just compute cos(n pi) explicity, it's simple enough

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last slate
midnight plankBOT
last slate
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can anyone explain question 17 for me

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i am new to limits thats why i am asking

surreal moon
midnight plankBOT
rough birch
surreal moon
rough birch
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oh wait its 0

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L'Hopital's rule?

snow iron
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could try using the conjugate

last slate
rough birch
last slate
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yes

surreal moon
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l'hopital would work, but tbh with radicals, the work involved would not be radical sad

last slate
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thank u guys finally got the answer

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upbeat plinth
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inner wolf
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You need to set the derivative of that to zero, to find critical points

outer saffron
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2

midnight plankBOT
# outer saffron 2

As a helper, please do not give out answers that could be copied as a homework solution. Have the student work through the problem themselves and guide them along the way.

upbeat plinth
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subtle torrent
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I think it's E

upbeat plinth
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outer saffron
subtle torrent
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Yah for the second question you can also adopt this strategy, it's very quick @upbeat plinth

upbeat plinth
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subtle torrent
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? Isn't noobmaster already said?

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You can't see his msg?

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outer saffron
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subtle torrent
blazing pike
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hello im new in server

outer saffron
outer saffron
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grand pondBOT
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lavish venture
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spider-man pjs

upbeat plinth
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lavish venture
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brother why are you using quotient rule

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distribute the 1/x

upbeat plinth
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lavish venture
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reduce the powers

upbeat plinth
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fallow scarab
upbeat plinth
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lavish venture
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f(x) = x^2 - 4x + 7

upbeat plinth
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lavish venture
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f’(x) = 2x - 4

upbeat plinth
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lavish venture
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what

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$\frac{x^3-4x^2+7x}{x} = \frac{x^3}{x} -\frac{4x^2}{x} + \frac{7x}{x} = x^2 - 4x + 7$

grand pondBOT
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ember sage
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The theta in the bracket means it’s in the fourth quadrant right

subtle gulch
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yes

ember sage
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Thx

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keen seal
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when we have a row or column that repearts in a matrix in linear algebra

keen seal
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does that mean theres no solution?

sharp coral
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it depends

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sometimes it might mean infinite solutions

keen seal
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<@&268886789983436800>

analog vine
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no screenshot necessary for future reference, we can see deleted messages

keen seal
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oh ok

midnight plankBOT
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low stream
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Hi, I am want to show that for $A = {x \in \mathbb{R} \mid x^2 < 2}, (\sup{A})^2 = 2$.

My work: Use trichotomy to prove a contradiction in other two cases where $ (\sup{A})^2 > 2$ and $ (\sup{A})^2 < 2$.

(i will refer to lub as z) First assume that square of lub is greater than 2. that means lub is greater than sqrt(2). then, take $\epsilon = z - \sqrt{2} > 0$. Then, for $w = z - \frac{\epsilon}{2} < z$, since $z$ is lub then $w \in A$. Then, $w^2 = (z - \frac{\epsilon}{2})^2 = z^2 - z\epsilon + (\frac{\epsilon}{2})^2

Basically I aim to show that there will be an upper bound smaller than $z$ if we assume it to be greater than sqrt(2) and there is a least upper bound which is greater if we assume $z$ to be less than sqrt(2), but i am not sure how to flesh that out in the details.

grand pondBOT
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shell
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low stream
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i know that i want to find that if z is the lub then if we assume z to be less than 2 and take w > z then we want to show that w is in A (which contradicts the fact that it cannot be in A if z is to be the lub) and similar for z being greater than 2

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just not sure how exactly to execute the idea

midnight plankBOT
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@low stream Has your question been resolved?

rugged saffron
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The idea is to show that sup(A)^2 >= 2 and sup(A)^2 <= 2. Call M=sup(A), so first suppose M^2 < 2. The idea to contradict this is to find a real number x > M such that x^2 < 2. You will have to consider the interval (M^2, 2)

low stream
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or sorry i meant w < M for w = M - epsilon

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then i wanted to show that w^2 > 2

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which implies w is not in A

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which implies z is not

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lub

rugged saffron
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Firstly, I think the point of this exercise is to show that sqrt(2) actually exists, so we should probably not use it in the proof. If we assume M^2 > 2, the contradiction we are looking for here is that there exists a delta > 0 such that $(M-\delta)$ is also an upper bound for A, as then M would not be the least upper bound. I think this is what you are trying to do right?

grand pondBOT
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low stream
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thats what i wanted to do

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then i was going to show that this quantity squared is greater than 2 which means it is not in the set

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but the answer key uses sqrt(2)

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and answer key doesnt really make sense to me

rugged saffron
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Okay yeah they aren’t actually giving you epsilon in terms of what I have called M. But the overall idea is that if M > 2, then there is something just below that satisfies x^2 > 2. And on the other hand, if M < 2, there is something just above that satisfies x^2 < 2. In the second case, M is no longer an upper bound

low stream
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ii get the concept but i dont really get how the epsilon comes into play

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maybe that means i dont get the concept idk

rugged saffron
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I think they have skipped some working to show you what they have done. We are just trying to quantify this small nudge from M. If I want (M - delta)^2 > 2, then I just expand this bracket and try to rearrange for delta in terms of M

low stream
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Ok so we nudge down to show that there is a least upper bound smaller than M right

rugged saffron
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Yes that’s correct

low stream
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and we get to that conclusion by showing that if we take z^2 > 2 and w < z then we find that w^2 > 2 ( because we assume that the lub^2 is > 2) that this contradicts the fact that z is the lub

rugged saffron
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Yes but be careful with wording. We are saying given z, there exists a w < z such that bla. The goal of this part of the proof is to construct this w and show it satisfies that property of w^2 > 2

low stream
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right yes

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so when we take w as z minus some epsilon and find its square, im not sure how they find that the square is greater than 2

rugged saffron
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Yeah this is not a given and your proof just shoves it under the rug by saying “when epsilon is small…”

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If you wanted to be rigorous you would have to say “epsilon must be this small”

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That’s the idea of the proof

low stream
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im not sure then why they take epsilon to be z - sqrt 2

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that. seems arbitrary

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or is that the whole point

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that they inadvertantly aim to contradict the fact that epsilon is greather thgan 0?

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when it is actually equal to 0

rugged saffron
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Yeah the point is that if z is not equal to sqrt(2) we have a positive epsilon distance between them, work with this, get a contradiction

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It’s a fairly common idea

low stream
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ah i see

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i get that part but im not sure how the computation works out to getting w^2 > 2

rugged saffron
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If you just think about it completely concretely with a number line the contradictions become clearer I think. If the lub is < sqrt(2), then the midpoint must have square >=2, but this is absurd

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e.g. suppose 1.4 is the lub for A

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We know sqrt(2) = 1.414….

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So this logic would say that 1.41^2 > 2

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But this is just not true

low stream
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ok so in the case where lub > 2 if we say lub is 1.5 is the lub we can say like 1.45 is less than the lub but 1.45^2 is also greater than 2 right

rugged saffron
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Yeah exactly

low stream
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and we can do this infinite times because sqrt2 is not in the rationals

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makes senes

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well ig we. can do this infinite times if sqrt2 waws in the rationals

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but we would never get an answer since it is not

rugged saffron
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I don’t know what you mean by infinite times, just this always works if you assume either lub < sqrt(2) or lub > sqrt(2). This has nothing to do with sqrt(2) being irrational, I could do the exact same thing with sqrt(4)

low stream
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yeah i meant like we will not get an actual answer, ik we can do it infinite times for anything

rugged saffron
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Okay yeah, the point of these proofs is that I could choose M to be anything and this would give me the recipe for contradiction

low stream
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right yeah

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but i dont really udnerstand the symbolic version in the answer because if w^2 is greater than z^2 ( a number which is greater than 2) minus a positive number, that doesnt mean w^2 is greater than 2

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are we just assuming epsilon is small enough to make this true

rugged saffron
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But how small is that positive number

rugged saffron
low stream
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i see

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that feels a bit unsettling but

rugged saffron
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As I said, your solutions are not fully detailed

low stream
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yeah

rugged saffron
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There is a way to be completely convincing

low stream
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i assume thats beyond the scope of my class

rugged saffron
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No when I learned it in an equivalent class they supplied a proof

low stream
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i see

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can i ask another question

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my professor gave this weird proof for showing that set of rationals whose squares is less than 2 does not have a least upper bound in rational numbers

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this seems like a very inelegant way and it also doesnt really make sense to me

rugged saffron
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Yeah tbh it is quite a lot of jargon to get your head around, it would take me a while to fully digest. What you could do to prove this fact is use what you have just done above with showing sup(A)^2 = 2, and use the uniqueness of supremum. We already know sqrt(2) is irrational, so this is a proof

rugged saffron
# low stream

But the principle of this argument is very common. Assume for contradiction, conclude either that it is not an upper bound, or not the least upper bound

low stream
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yeah my initial thought was to just use what i did above and then we know sqrt2 is irrational but i think this proof assumes the same but gets to the conclusion in a different way

rugged saffron
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Yeah so the strategy is sort of the same, instead of nudging by a real number delta, they are nudging by a small enough 1/n, which ensures that we stay rational

low stream
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is this the archimedean property

rugged saffron
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Yeah it is

low stream
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these notes are weird it introduces the property after this example

rugged saffron
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Yeah that’s weird, it’s basically one of the first properties of R you should learn

low stream
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yeah

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thanks for the help

rugged saffron
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No worries, hope it is at least a bit clearer

low stream
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yeah helped a lot was stuck on this for a while

midnight plankBOT
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gaunt jetty
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Both the poisson and normal distributions are able to approximate the binomial distribution

gaunt jetty
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My question is, how does one decide between which approximation to choose?

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upbeat plinth
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tidal turret
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the linearization is the tangent line at x = a

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tidal turret
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ye

upbeat plinth
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tidal turret
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the linearisation is an approximation of the function at the point, so it's not going to be exact

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you need to differentiate tan aswell

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tidal turret
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L(x) ≈ tan(-pi/4) + sec^2(-pi/4)(x+pi/4)

upbeat plinth
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tidal turret
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L(x) ≈ tan(-pi/4) + 2(x+pi/4)

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tidal turret
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gaunt jetty
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gaunt jetty
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Am i just incorrect or their integration variables are incorrectly placed?

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shouldnt it be dydzdx under their configuration, or something?

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actually, i have no idea what they're doing in there. Their way of evaluating the integral is completely flying over my head

untold rune
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That's typo

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You're right.

gaunt jetty
#

.close

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vague marsh
midnight plankBOT
vague marsh
#

Should this problem have two solutions or just one?

#

They only advise the above x = 30° + n * 120° is the answer

#

But shouldn't we apply both identities?

last arch
# vague marsh

It's the fact that the basic angle just happens to be 90

#

And 180-90=90

#

So that solution just happens to be included in the given solution

vague marsh
last arch
#

Try just 0*60-30=-30deg as a test case

#

How'd you get that one

vague marsh
last arch
#

I mean just plug -30 degrees into the equation

#

And check if it works

vague marsh
#

OH you mean the original one

#

Now i see

last arch
#

How'd you get that solution

#

x=60*n-30

vague marsh
#

You mean like this in the original equation?

last arch
#

Yea

vague marsh
#

Sorry -30*

#

Now I see

last arch
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twilit field
#

If There exists a $c \in \R$ such that $a<c<b$ for all $a \in A, b \in B$ then $sup(A) < inf(B)$.
\
I'd try a proof by contrapositive. If $\sup(A) \geq inf(B) $, then there exists $a \in aA, b \in B$, suhc that $a \geq c \geq b ; \forall c \in \R$

grand pondBOT
#

ƒ(Why am. I here)=I don't Know

twilit field
#

Does this sound right so far

runic hamlet
#

no

#

a statement like a >= c for all c clearly cant work

#

(among other issues)

twilit field
#

logically

runic hamlet
#

you didnt negate correctly

#

if that is your question

#

$\exists c\in\bR: (\forall a\in A: a<c)\land (\forall b\in B: c<b)$

grand pondBOT
#

Denascite

runic hamlet
#

thats the statement you have to negate

twilit field
#

So the negation would be $\forall c \in \R : ( \exists a \in A : a \geq c) \lor ( \exists b \in B : c \geq b)$

grand pondBOT
#

ƒ(Why am. I here)=I don't Know

twilit field
#

If $sup(A) \geq inf(B)$, then $\forall c \in \R : ( \exists a \in A : a \geq c) \lor ( \exists b \in B : c \geq b)$

grand pondBOT
#

ƒ(Why am. I here)=I don't Know

twilit field
#

This is false consider $A =[0,1] , B= [0.5,1]$. Clearly $\sup(A)= 1$ and $inf(B)=0.5$, This statement is clearly not true for all $c\in \R$

grand pondBOT
#

ƒ(Why am. I here)=I don't Know

indigo stone
visual tiger
twilit field
#

so I decided to try to prove the contrapositive

visual tiger
#

I don't think I understand your counterexample still

runic hamlet
#

well its wrong. so that doesnt help

twilit field
#

How's it wrong

runic hamlet
#

why do you think otherwise

#

dont say "clearly"

twilit field
#

Yeah, misread the second part

#

oops

#

I feel like this is going to be even harder to prove, being a forall statement

#

hmm

visual tiger
runic hamlet
#

shhh

visual tiger
runic hamlet
#

you said whether the statement is true or not

#

which really is the hard part of true/false questions

twilit field
#

I can't talk about the infimum ans supremums of infty

#

can I

#

Let $B= [0,1], A=[0.5, 1.5]$

grand pondBOT
#

ƒ(Why am. I here)=I don't Know

twilit field
#

nvm, bad counter example

#

[0,2), (2, 3] Works as a counter example, doesn't it

runic hamlet
#

why

twilit field
#

2 is greater than all elements in A and less than all elements in B, so c=2

#

but sup(A) = inf(B)

#

Cool

#

Thanks!

#

.close

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#
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twilit field
#

The uniquness part is confusing me

midnight plankBOT
twilit field
#

I'm unable to understand this

#

is uniquness because composition of functions is always associative

#

<@&286206848099549185>

#

.close

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hoary urchin
#

https://prnt.sc/VDBWKoEdn6MC This screen has the question i am a bit confused about, from what I have done so far I am confident in a-c but for d/e i am not 100% certain my answer is right. I got part d as 0.00000054842, and for part e i believe this is just ^3 since there are 3 independent starting points

Lightshot

Captured with Lightshot

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#

Please don't occupy multiple help channels.

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last slate
#

How can I resolve this ? I have no idea and I need it. Using guides and AI doesnt help me

last slate
#

It's maybe too easy for you but I dont understand anything

carmine sigil
#

If you just need to solve for z, then a first step is typically to clear all of the fractions. You can multiply both sides of the equation by 10(z+2)(z-4) to do this.

silent parcel
summer ravine
#

Firstly, make the two fractions into a single one on the L.H.S. For that, you need to take a number of both (z+2) and 10. So you shall just multiply them out. Now adjust the numerators accordingly. Now, use the fact that: if a/b = c/d, then ad = bc

midnight plankBOT
#

@last slate Has your question been resolved?

silent parcel
summer ravine
#

Open your own channel

silent parcel
#

That’s a solution

summer ravine
#

Ok

last slate
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last slate
#

Ty all

midnight plankBOT
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fierce canyon
#

factorise fully (x^2-x-6)(x^2+3x-4)+24

midnight plankBOT
flat plinth
#

well first expand to see if the 24 can be factorise once its added to the other constants

#

!status

midnight plankBOT
#
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
flat plinth
fierce canyon
#

I got 2

#

My teacher told me to factorise both brackets first but then I get stuck

fierce canyon
flat plinth
#

if youve never done a quartic does your teacher just want you to ignore the +24?

fierce canyon
#

He still wants it

#

So I’m a bit confused abt it

flat plinth
#

if you dont factorise from a qaurtic

#

the furthest you can get is

#

$(x-3)(x+2)(x+4)(x-1) + 24$

grand pondBOT
#

Nyxzore

fierce canyon
#

Yeah that’s where I’m at currently

#

<@&286206848099549185>

fallow scarab
#

are you supposed to use vieta's formula

fierce canyon
#

I’m not too sure

flat plinth
fierce canyon
#

but im not too sure how to factrosie

flat plinth
#

use law of natural roots

fallow scarab
#

i think also from here you can guess what x

#

24 = 2 * 2 * 2 * 3

fierce canyon
fallow scarab
#

so some small negative integer should work

#

and probably also small positive number too

fierce canyon
#

How do we factorise this tho?

fallow scarab
#

find two roots using ^ then polynomial/synthetic division it out then quadratic formula the rest

flat plinth
#

The idea is that if you plug f(Z) into a function f where Z is an integer if f(Z)=0 then x-Z is a factor

fierce canyon
#

im a bit confused abt this srry

#

im a bit new to learning about this sry

fallow scarab
fallow scarab
midnight plankBOT
#

@fierce canyon Has your question been resolved?

fierce canyon
#

<@&286206848099549185> im still rlly stuck

fallow scarab
fierce canyon
#

i dont understand what to do

fallow scarab
fallow scarab
#

plug in x=-1,-2,-3

fierce canyon
#

what am i meant to find by plugging in

fallow scarab
#

there shouldn't need to repeat something already explained when you can just scroll up and read

fierce canyon
#

i didnt really understand what he meant

fallow scarab
#

.............

fallow scarab
fierce canyon
#

-1 is 48

#

-2 is 24

#

-3 is 0

#

@fallow scarab

fallow scarab
#

you found a root, -3

#

so you found one of the factors

fallow scarab
fallow scarab
#

x=1,2,3

fierce canyon
#

1 is 24

#

2 is 0

fallow scarab
fierce canyon
#

how would we do that step?

fallow scarab
#

.......

#

did you find your two factors? because you can't do the division until you figure them out

fierce canyon
#

wasnt it (x-3) and (x+2)

#

but the video only shows it using one factor

fallow scarab
#

process is the same

midnight plankBOT
#

@fierce canyon Has your question been resolved?

fierce canyon
#

.close

midnight plankBOT
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dim anchor
#

How to find integral on 5)

midnight plankBOT
dim anchor
#

so i have to find integral on tan^2 first?

#

.close

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obtuse totem
#

hello

midnight plankBOT
obtuse totem
#

i dont think i have question yet

#

but pls lemme stay in the channel

#

i got absolutely DESTROYED in my complex analysis exam

#

took a massive day off for break

#

but im feeling so defeated and so unmotivated

#

staying here will keep me accountable

#

also like again all my friends are getting internships i havent heard back from anything im feeling so worthless rn

fallow scarab
#

#therapy

obtuse totem
#

like absolute sht

last arch
#

Rip

obtuse totem
#

yup yup

fallow scarab
#

If only that was a real channel

last arch
#

Bro needs to seek professional counselling ong

obtuse totem
#

frfr

#

i got a massive cup of coffee and like nice candles and some chocolate i still feel horriblle

#

been on my phone for the whole day ngl

#

its bad

last arch
#

Melt the chocolate into the coffee

lavish venture
obtuse totem
#

fr

#

actually

#

its bad for my mental health

last arch
#

Go take a walk or something

#

Frfr

lavish venture
#

quality of life depends on academic results

#

🔥🔥

last arch
#

Unless you live in those kind of suburbs

#

Where there are like no side walks

obtuse totem
#

its freeing rn where i live

#

i do not wanna go out😭

last arch
#

It's like a ice bath

lavish venture
#

just exercise bruh

obtuse totem
#

bruh too late now gyms closed and its so cold

lavish venture
#

unfortunate

#

do something easy

obtuse totem
#

yea😔 i just feel so uncapable of anything

#

because theres nothing to show for it

#

and social media is bad like rlly bad

torn flint
#

Turn the device off and do something to get the blood flowing

obtuse totem
#

its making me want to take an "easier route"

#

i need to just stop

#

and start studying for my next exam cause all im doing is complaining

#

i just need a good cry

#

whats wrong wme😭

torn flint
#

Turn off the device

#

We are not your therapists

obtuse totem
#

true

lavish venture
obtuse totem
#

which is why Im gonna start studying now

#

i'll have questions fs

#

for this question, we learnt to guess particular solutions (in this case a polynomial, A/x) but the method only works if its constant coefficients in front of y'', y', and y

#

so what should you do when theres polynomials in front of ys

#

oh nvm

#

question only asks for the particular sol, so you dont need the homogenous part

#

so not the c1y1+c2y2 part

robust isle
#

try A/x anyway @obtuse totem

obtuse totem
#

yup! I got it

midnight plankBOT
#

@obtuse totem Has your question been resolved?

midnight plankBOT
#

@obtuse totem Has your question been resolved?

obtuse totem
#

not sure how they simplified it lol

#

oh wait

#

im good

#

everything was good until the integral😭

#

i keep making these mistakes

#

you know, if I actually get my degree,

#

that would be the most insane thing ever

fallow scarab
obtuse totem
#

facts😤

#

i may be stupid but im still trekking along🤩

#

you know what maybee i take a break and do more questions later

#

thank you for tuning into my beauuutiful life story byeeeeeeeee

#

.close

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#
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tidal turret
midnight plankBOT
tidal turret
#

Let $P(x) = x^3 - 2x^2 + 3x - 6$. Find the polynomial $Q \in \mathbb{R}[x]$ of minimal degree such that the polynomial $H = P \cdot Q$ has one triple root and two double roots, and $H(-1) = 27$.

grand pondBOT
#

938c2cc0dcc05f2b68c4287040cfcf71

grim vector
#

What are the roots of P(x) ?

midnight plankBOT
#

@tidal turret Has your question been resolved?

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midnight plankBOT
grim vector
#

<@&268886789983436800>

misty gorge
#

please don't troll in the help channels

#

.close

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#
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flat plinth
#

then youre violating discord's tos bro

grim vector
late hill
#

ok bye then

analog vine
#

💣

flat plinth
#

danko

midnight plankBOT
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vestal moth
#

need help with this:
Prove
Q(k): C¹ₖ₋₁/(k-1)-C²ₖ₋₁/(k-2)+C³ₖ₋₁/(k-3)+...+(-1)ᵏ⁻²⋅Cᵏ⁻¹ₖ₋₁/[k-(k-1)]+(-1)ᵏ⁻¹⋅Cᵏₖ/k=1/k
which can also be written as
1-(k-1)/2!+(k-1)(k-2)/3!-(k-1)(k-2)(k-3)/4!+...+(-1)ᵏ⁻²+(-1)ᵏ⁻¹⋅1/k=1/k

Q(2):1-1/2=1/2 true
Q(3):1-2/2!+1/3=1-1+1/3=1/3 true
Q(4):1-3/2!+3⋅2/3!-1/4=1-3/2+6/6-1/4=2/2-3/2+(1-1/4)=-1/2+3/4=-2/4+3/4=1/4 true

No idea how to prove Q(k-1)⇒Q(k).

Q(k-1): 1-(k-2)/2!+(k-2)(k-3)/3!-(k-2)(k-3)(k-4)/4!+...+(-1)ᵏ⁻³+(-1)ᵏ⁻²⋅1/(k-1)=1/(k-1)
Q(k): 1-(k-1)/2!+(k-1)(k-2)/3!-(k-1)(k-2)(k-3)/4!+...+(-1)ᵏ⁻²+(-1)ᵏ⁻¹⋅1/k=1/k

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@vestal moth Has your question been resolved?

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@vestal moth Has your question been resolved?

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@vestal moth Has your question been resolved?

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@vestal moth Has your question been resolved?

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tidal turret
#

Let $P(x) = x^3 - 2x^2 + 3x - 6$. Find the polynomial $Q \in \mathbb{R}[x]$ of minimal degree such that the polynomial $H = P \cdot Q$ has one triple root and two double roots, and $H(-1) = 27$.

grand pondBOT
#

938c2cc0dcc05f2b68c4287040cfcf71

tidal turret
midnight plankBOT
#

@tidal turret Has your question been resolved?

midnight plankBOT
#

@tidal turret Has your question been resolved?

midnight plankBOT
#

@tidal turret Has your question been resolved?

fierce rain
tidal turret
#

how

#

we dont know any roots of P(x)

#

ah, you mean use rational root theorem?

#

dont tell me its rational root theorem

fierce rain
#

i am just giving you ideas, but 2 is a trivial root

#

so apply euclidean division, P(x) by x-2

#

and you get the rest of the factors

#

so already you have 2, and have options to turn 2 into a triple or double root based on your choice of Q

tidal turret
#

2 is a trivial root? wdym

#

how did you got that root?

fierce rain
#

just plug it in man, its a small number that happens to verify that its a root

tidal turret
#

?

fierce rain
#

2^3 - 2x2^2 + 2x3 - 6

tidal turret
#

how did you got it

fierce rain
#

its not important, you are distracting yourself from the question

#

but if you really insist:
x3-2x2+3x-6
x2(x-2)+3(x-2)
(x-2)(x2+3)

#

happy?

#

@tidal turret

tidal turret
#

I guess I am happy

tidal turret
grand pondBOT
#

938c2cc0dcc05f2b68c4287040cfcf71

fierce rain
#

now the next step is to calculate P(-1)

#

we get that P(-1)= -12

#

-1 CANT be a root for Q(x) because that would mean H(-1)=0

tidal turret
#

,calc (-1)^3 -2(-1)^2 + 3(-1) - 6

grand pondBOT
#

Result:

-12
fierce rain
#

so you have to construct Q(x) so that Q(-1)= -27/12 , Q(2)=0 and a root "a" of your choice is triple

#

we have that Q(x)=(x-2)Q' with Q'(x)=k(x-a)^3

tidal turret
#

what does Q' denote? the first derivative of Q(x)

fierce rain
#

no, just a factor of Q

#

it will be the factor with a triple root

#

H(-1)=P(-1)Q(-1)
27=-12(-3)Q'(-1)
27/36=Q'(-1)

#

we now found a condition on Q'

#

k(x-a)^3 = 27/36 = 3/4 x=-1

tidal turret
#

H(-1)=P(-1)Q(-1)
27=-12(-3)Q'(-1)

#

how did this happen (-3)Q'(-1)

fierce rain
#

Q(x)=(x-2)Q'(x)

#

replace w -1

tidal turret
fierce rain
#

by construction

tidal turret
#

how in the world

fierce rain
#

just re-read my messages

#

you have problems following, let me get a paper

#

but the reason is simple

#

H needs to have a double root and a triple root

#

P already has a root which is 2

tidal turret
#

why is 2 a root for Q

fierce rain
#

Q needs to be the smallest degree possible, so its in our interest to construct Q so that 2 is also a root

#

we want 2 to become the double root OR triple root

#

i chose for 2 to be the double root

#

therefore we get Q(x)=(x-2)Q'(x)

#

with Q' being a certain polynomial that has a triple root, since thats the goal

#

do you follow?

tidal turret
#

wait a second, H = P.Q has to have a triple root and two double roots

#

how is Q related to the double roots

#

we found P has a root at x = 2

fierce rain
#

oh two double roots, i have misread, well nothing changes anyways

fierce rain
tidal turret
#

gimme a second

fierce rain
#

because H needs to be of a minimal degree

tidal turret
#

,w x^2 +3 =0

fierce rain
#

they are complex solutions

tidal turret
#

P has one real root and two complex

fierce rain
#

i dont know if the question imposes for them to be real or not

#

is there any other context provided?

tidal turret
#

in order for Q to be minimal polynomial we repeat the root of x = 2 for Q
since H = P.Q has a triple root and two double roots

#

we can repeat the complex roots but is easier if we repeat x = 2

fierce rain
#

actually it would be advantageous to repeat the complex roots

#

because that already gives us two double roots

tidal turret
#

lets repeat the complex roots then

fierce rain
#

alright then

tidal turret
#

,w x^2 +3 =0

fierce rain
#

this means

grand pondBOT
fierce rain
#

Q(x)=k(x-2)^2(x^2+3) = k(x-2)P(x)

#

we only need to find k for the condition on H

#

H(-1)=P(-1)Q(-1)
27= k(-3)P(-1)P(-1)
27=k(-3)(-12)(-12) blablabla

#

k=-27/432

#

k=-9/144

tidal turret
#

,w expand (x-isqrt(3))(x+isqrt(3))

fierce rain
#

k=-1/16

#

therefore

#

Q(x)=-1/16(x^2+3)(x-2)^2

fierce rain
tidal turret
#

27=k(-3)(-12)(-12)

#

,calc -3*-12*-12

grand pondBOT
#

Result:

-432
fierce rain
#

,calc 27/432

grand pondBOT
#

Result:

0.0625
fierce rain
#

yea thats 1/16

tidal turret
#

2 is the triple root

#

and the two complex roots from P are the two double roots

#

for Q

fierce rain
#

yes

#

and scalar k is -1/16 to satisfy that H(-1)=27

tidal turret
#

,w expand (x-2)(x^2+3)

grand pondBOT
tidal turret
#

I understood, but It wasn't easy

fierce rain
#

it comes with time

#

dont think in terms of theorems, its more liberating, you should only draw them last

#

sometimes solutions are just infront of you

tidal turret
#

yeah

#

.solved

midnight plankBOT
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grave summit
midnight plankBOT
grave summit
#

i dont even know where to begin with this

#

i looked it up and it said smth abt Ricatti equations - but this is meant to be an interview problem so

#

what's going on here

wide isle
#

I am not too good at these; maybe this observation helps: sometimes, when you have dy/dx = y^2, the solution uses the property of a/x acting similarly when differentiated and squared.

grave summit
#

oh i see a bit?

wide isle
#

although I am not 100% it's useful here.

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#

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verbal kindle
#

$$I=\int^{\pi}_{0}\dfrac{x|\sin 2x|}{3+\sin^2 x},dx.$$

grand pondBOT
#

Amadeus

verbal kindle
#

how do you even approach this

midnight plankBOT
#

@verbal kindle Has your question been resolved?

verbal kindle
#

.close

midnight plankBOT
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dense idol
#

substitution u=pi-x would be good

midnight plankBOT
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young pelican
#

is this integral converge conditionally? and if does how to prove it?

uneven sandal
#

it does converge, you can check this by splitting up your integral in 3 parts

1 from 0 to epsilon
1 from epsilon to N, where N is a big finite number
1 from N to infty

#

for very small x the sqrt(x) term will dominate, and for very large x the x term will dominate in the denominator

midnight plankBOT
#

@young pelican Has your question been resolved?

young pelican
uneven sandal
#

the dirichlet's test is perfect for this, for example one can show that

$\int_1^{\infty} \frac{\sin(x)}{x} ,dx$ is convergent using the Dirichlet test, which is similar to your problem.

grand pondBOT
young pelican
#

ok ty

midnight plankBOT
#

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last hatch
#

Martha arranged books on two shelves with the same internal dimensions. All the books were the same size. She filled the first shelf (I) completely with 12 books. On the second shelf (II) she decided to arrange the books side by side across the entire width of the shelf so that there was free space above them, as shown in the drawing.

Note: the drawing shows the first shelf completely filled with books (I) and the second shelf partially filled with books (II).

How many books at most could Martha fit on the second shelf (II) with the arrangement shown?

A) 7
B) 8
C) 10
D) 11

last hatch
#

6b = 21 cm

#

b = 21/6

#

b = 3,5 cm

#

28/3,5 = 8

#

So she can fit 8 books?

#

B)?

#

<@&286206848099549185>

hearty rune
#

seems logically sound

remote merlin
#

Hi

last hatch
midnight plankBOT
# last hatch <@&286206848099549185>

Please only use the <@&286206848099549185> ping once if your question has not been answered for 15 minutes. Please do not ping or DM individual users about your question.

last hatch
#

angerysad 🍉

#

🤬🤬🤬🤬🤬

midnight plankBOT
#

@last hatch Has your question been resolved?

midnight plankBOT
#

@last hatch Has your question been resolved?

midnight plankBOT
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fervent storm
midnight plankBOT
fervent storm
#

answer is 152 but how teacher didnb give explanation

lucid dew
#

since AB is parallel to CD, angle BDE is 76

fervent storm
#

mhm

thorn sorrel
#

x is angle d + b

lucid dew
#

because ABD and BDE are alternate interior angles

#

and angle BDE is equal to angle DBE since triangle DBE is isosceles

#

so angle BED is 180-76-76=28

#

x is 180-BED=180-28

fervent storm
#

ohhhhh

#

thank you!

lucid dew
#

ofc

#

.close

#

.solved

rain wasp
#

no perm moment

fervent storm
#

.close

midnight plankBOT
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tidal turret
#

One gear turns $33\frac{1}{3}$ times in a minute. Another gear turns 45 times in a minute. Initially, a mark on each gear is pointing due north. After how many seconds will the two gears next have both their marks pointing due north?

grand pondBOT
#

938c2cc0dcc05f2b68c4287040cfcf71

sharp wave
#

Have you tried finding their angular velocity

#

and proceeding from there?

tidal turret
#

is lcm lcd exercise not related to physics btw

#

but if you want we can look for angular velocity

sharp wave
tidal turret
#

both are fine tbh

#

!nosols

midnight plankBOT
#

As a helper, please do not give out answers that could be copied as a homework solution. Have the student work through the problem themselves and guide them along the way.

last arch
#

Mb I mean

sharp wave
#

alright so after finding w, you can do is 2pi* n1 = w1* t and 2pi* n2 = w2*t

#

n1 and n2 are just any natural numbers

last arch
#

And we're trying to find the t when both functions are whole numbers

tidal turret
#

I need more handhold

#

how do I find the w velocity

#

how do I find the t such that both functions are whole

sharp wave
#

do you know what w is

soft latch
#

I feel like finding w is MASSIVELY overcomplicating an LCM problem...

#

Find out how many seconds it takes for each gear to make a full revolution, and find the lcm of those two numbers and you're done

#

100/3 times/min means it spins 600/3 = 200 times/sec, or it takes 1/200 seconds to spin once. the other is 45*60 = 2700times/min, or it takes 1/2700 seconds to spin once. just find lcm there and you're done

midnight plankBOT
#

@tidal turret Has your question been resolved?

radiant roost
radiant roost
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floral grail
#

can someone please explain why (B) is wrong

midnight plankBOT
lethal path
#

you don't know anything about f(2 * 2) = f(4)

#

f(4) could be anything!

floral grail
#

isn't there a limit property where you can pull out the constant

lethal path
#

you've confused $f(2x)$ with $2 f(x)$

grand pondBOT
lethal path
grand pondBOT
floral grail
#

ohh ok i got it

#

.close

midnight plankBOT
#
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floral grail
lethal path
grand pondBOT
lethal path
#

find the value of t

#

no need to sub the critical value of t back into f(t) - g(t), cause that would give you the max number of people

besides you don't know what f(t) and g(t) are without integrating

lethal path
#

it is indeed 7.888

#

there is another one at 10.974 yes but you can look at the graph

#

only t = 7.888 goes from positive derivative to negative derivative

#

so increasing then decreasing

floral grail
#

thanks

#

.close

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#
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twilit field
#

Show that if $a,b \in \Q$, then $a+b$ and $ab$ are also rational.
\
Proof: Suppose $ab$ is not rational. Let their product be $c$. We then have $ab = c$, or equivalently $a= \frac{c}{b}; b\neq 0$. However, a being rational is the quotient of two rationals, this contradicts that. Therefore $c$ cannot be irrational.

grand pondBOT
#

ƒ(Why am. I here)=I don't Know

drifting cloak
#

what is the question here?

tawdry laurel
#

I think

drifting cloak
#

oh

tawdry laurel
#

Makes sense

#

(the proof)

drifting cloak
#

i think it could be more rigorous

twilit field
#

Hmm, how?

drifting cloak
#

but intuitively it makes sense

tawdry laurel
radiant roost
#

you're assuming an irrational over a rational is irrational

drifting cloak
#

yeah that

radiant roost
#

then i don't see how you got a contradiction

#

what is the contradiction?

tawdry laurel
#

He assumed c is irrational

radiant roost
#

yes

tawdry laurel
#

And cant be expressed as real / real

radiant roost
#

wait

#

you're saying he showed c is rational, and that's the contradiction?

twilit field
#

oh

twilit field
#

I see the problem

radiant roost
#

i don't see anywhere he showed c is rational

zealous schooner
#

Yeah this is just a constructive proof, you didn't use the assumption that c is irrational anywhere

radiant roost
#

i agree a direct proof will work

twilit field
#

Hmm, okay

tawdry laurel
#

Ah i got confused

twilit field
#

let me think

radiant roost
#

you should use the definition of rational

zealous schooner
#

You're also assuming b != 0 which isn't really necessary

drifting cloak
#

if a is rational then a = p/q where p, q = ___?

tawdry laurel
#

W

twilit field
formal orchid
#

@twilit field Let a = x/y and b = m/n where x, y, m, n belongs to Z

radiant roost
#

it can be expressed as a quotient of two integers

#

but it can also be expressed other ways

twilit field
#

yeah

radiant roost
#

for example, as an irrational over an irrational

#

for example, 1/2 is rational but it's equal to sqrt(2)/(2sqrt2)

twilit field
radiant roost
#

no that's right

drifting cloak
radiant roost
#

you know xm is an integer and you know yn is an integer

twilit field
#

so I assume closure under multiplication of integers

radiant roost
#

yes

twilit field
#

I see

#

okay

radiant roost
#

we would normally build integers first before building rationals

#

so

#

we can assume integer properties

twilit field
#

My book doesn't do that 😭

#

but okay

radiant roost
#

i mean in theory, anyway

zealous schooner
twilit field
#

A rational is any number that can be expressed in the form p/q , where p,q are integers

drifting cloak
#

soz

#

im a statistician 😭

zealous schooner
radiant roost
#

hm

drifting cloak
twilit field
#

Let $a= \frac{p}{q}, p,q \in \Z$, $b= \frac{m}{n}; m,n \in \Z$
\
$\frac{p}{q} \frac{m}{n} = \frac{pm}{qn} =c \implies c \in \Q$

grand pondBOT
#

ƒ(Why am. I here)=I don't Know

twilit field
grand pondBOT
#

ƒ(Why am. I here)=I don't Know

radiant roost
drifting cloak
#

yeah

#

looks reasonable

twilit field
#

Cool, thanks!

#

I do something similar for addition

#

right

zealous schooner
zealous schooner
radiant roost
zealous schooner
twilit field
#

$\frac{p}{q} + \frac{m}{n} = \frac{pn+qm}{nq} = c$ again

grand pondBOT
#

ƒ(Why am. I here)=I don't Know

zealous schooner
#

You should probably prove this

radiant roost
#

are you talking about multiplication in Q or in Z?

twilit field
zealous schooner
#

You're assuming you know how multiplication and addition works in the rationals

twilit field
#

yeah, section 8.6 is a construction of R from Q

zealous schooner
#

But that doesn't constitute a proof I think

radiant roost
#

yeah, that should also be a matter of definitions, right?

radiant roost
#

shouldn't there be a definition of multiplication in Q that he can use?

zealous schooner
#

pq^{-1}mn^{-1}=pmq^{-1}n^{-1}

zealous schooner
radiant roost
#

that does seem more rigorous

twilit field
#

hmm

golden comet
#

what are we solving?

twilit field
#

We're done, I think

twilit field
golden comet
#

so proving a+b and ab are ratrional?

radiant roost
#

ye