#help-23

1 messages · Page 411 of 1

flat frigateBOT
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Azyrashacorki

soft lava
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I just don’t understand how it relates to the other problem cus this is how we did it in class but when I try to do it that way it did not work

quiet plume
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You have $20e^{-0.0001216t}$ and you want to know when you'll have half of what you started with (20)$

flat frigateBOT
#

Azyrashacorki
Compile Error! Click the errors reaction for more information.
(You may edit your message to recompile.)

quiet plume
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So you can write $10 = 20e^{-0.0001216t}$ and solve for t.

flat frigateBOT
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Azyrashacorki

quiet plume
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This will tell you the half life

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What did you get when doing this then?

soft lava
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I try to solve it but I get stuck here

quiet plume
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Then you can divide both sides by -0.0001216

soft lava
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570.02?

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On the answer key it is 5700 years so idk what I did wrong

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I double checked and I wrote down the original problem correctly

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I’m just really confused I don’t know what I did wrong even with the answer key

quiet plume
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You just lost a 0 transcribing

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Its -0.0001216

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Not -0.001216

soft lava
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Ohhh

quiet plume
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That should give you the right answer now

safe radishBOT
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@soft lava Has your question been resolved?

safe radishBOT
#
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honest idol
#

Hello , I need help with this problem please

upbeat veldt
#

Okay, so this is a standard optimization question in Calculus.

honest idol
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Yeah

upbeat veldt
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What is your understanding of optimization. What do you think the first thing we should do here?

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What are we trying to solve for?

honest idol
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We need to find our objective function and our constraint function

upbeat veldt
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Right, so we our trying to find the largest Volume we can obtain, so quantity is volume and we are maximizing it.

honest idol
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Yea

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w*l *h?

upbeat veldt
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Volume = LengthWidthh

upbeat veldt
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Now we need to rewrite it in terms of one variavble

honest idol
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Wdym

upbeat veldt
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So what relations do we know to rewrite it in terms of one variable?

honest idol
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Shouldn’t it be f(w,h,l) = whl

upbeat veldt
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We need to rewrite the volume in terms of one variable, so we can solve it and differentiate it.

upbeat veldt
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You can do that utilizing the other information you are given.

honest idol
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In similar problems I didn’t have to rewrite anything

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Ohhh btw

upbeat veldt
honest idol
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I’m doing Lagrange multipliers

orchid mirage
upbeat veldt
upbeat veldt
honest idol
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Yea

upbeat veldt
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Okay so to rewrite it in terms of one variable.

honest idol
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The problem is I have a test ina few hours and I didn’t learn it this way and I’m tryna build off of my previous knowledge so I don’t get too confused also because I’m lowkey running out of time

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So

upbeat veldt
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Well then you need to know this as this is essential

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Do you want me to give you the answer

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you may learn better that way

honest idol
quiet plume
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You already have the volume of the box as your objective function

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Now you have to write down your constraint equation

upbeat veldt
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Cost = 4sides + 1 top + 1 bottom
-> 4(l
h)2 + (lw)2 + (lw)*3
15 = 8(lh) + 2lw + 3lw

upbeat veldt
honest idol
quiet plume
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It’s really a constraint on the surface area you’re given

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So you need to find the cost of the box in terms of l, w and h and then your constraint says this cost is fixed at 15$

honest idol
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Idek 😂

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I mens

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Mean*

quiet plume
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Sketch out the box. You need the surface area of the top and sides along with the surface area of the bottom

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I need to bike home I’ll be back in 20min

honest idol
safe radishBOT
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@honest idol Has your question been resolved?

quiet plume
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Okay have you got a sketch?

honest idol
quiet plume
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Okay I feel it's hard to see what's going on with this. I was expecting more a 3d sketch

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Now you need the surface area of the bottom, and the surface area of everything else

honest idol
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so how are we doing that here

burnt notch
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Don't overthink

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Do you need to maximise the volume? Then, well, you have to write the volume formula, using some suitable variables

burnt notch
# quiet plume

So with these names for the main dimensions, can you write down the volume formula?

burnt notch
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Good

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Now., with your own words, what is the constraint for this problem?

honest idol
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i didnt really give anything besides the volume formula

quiet plume
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Say we disregard the fact that the cost must be 15$ for a second.
Can you write down what the area of the bottom side would be in terms of those variables ? What does this part cost then?
Can you write down what the surface area of the rest of the box is (without its bottom)? What does this part cost?

honest idol
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idk about the cost part tbh

quiet plume
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l*w is correct for the bottom

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But for the rest your box should also have a top.

honest idol
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Oh there fixed

quiet plume
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Okay.

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They're telling you the bottom costs 3$ per unit area to make.

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How much does the bottom cost?

honest idol
quiet plume
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So the bottom has area 1?

honest idol
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Oh wait

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Okay so how did we know cm^2 is our unit area

quiet plume
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You can assume w, h, l are given in cms, it doesn't matter.

honest idol
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Oh alright

honest idol
quiet plume
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If I tell you the area of the bottom is 4 cm^2, how much does the bottom cost to make if it costs 3$ per cm^2?

quiet plume
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Right, so you multiply the area by the cost per unit area to get the cost.

honest idol
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wait so its 2(wh) + 2(lh) + lw = 12

quiet plume
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The whole point of the setup is to express the total cost of the box in terms of w,h and l. You have no equation yet since the constraint is specifically a constraint on the total cost of the box.

honest idol
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true

quiet plume
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So I'll ask again. If the bottom of the box has area w*l and you're given that the bottom costs 3$ per unit area to make, what is the cost of the bottom of the box?

quiet plume
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It's the same thing as here but with w*l instead of 12.

honest idol
quiet plume
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The thing is you answered it with a fixed number.

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For a bottom with area 4 cm^2, you said that the cost was 4 * 3 = 12$

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For a bottom with area w*l cm^2, it's not a different process.

quiet plume
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Good. So the bottom costs 3wl to make.

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Now you need to compute the cost of the rest of the box.

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You computed its area earlier

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And you know it costs 2$ per cm^2.

honest idol
quiet plume
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Good. So the rest of the box costs 2(2wh + 2hl + wl) to make

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What is the total cost of the box, then?

honest idol
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2( 2(wh) + 2(lh) + lw ) + 3(wl)

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= 4(wh) + 4(lh) + 2lw + 3wl

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= $15

quiet plume
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Yes, so you have your constraint given by 4wh + 4hl + 5wl = 15.

honest idol
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ohhhhhhh

honest idol
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the constraint equation is kinda confusing

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is it not supposed to be expressed in the way im expressing it?

burnt notch
honest idol
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because of the = 15

burnt notch
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How's it troubling you?

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You can (and should) bring the 15 to the left hand side

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So that you have g = 0, where g is your constraint equation

honest idol
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your constraint equation is always in the form g = c?

burnt notch
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No 😭

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Remember what Azy told you yesterday?

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It is of the form "g(...) = 0"

burnt notch
honest idol
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thats after differentiating it or what

burnt notch
honest idol
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yeah i think im confusing the = 0 part but thats just f(x,y) = z

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such that z = 0

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so its not really different from any funciton in space

burnt notch
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Wait wait

honest idol
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well that was a bold claim

quiet plume
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Whatever you get as your constraint, (expression)(x,y,z) = c, you can always rewrite it as g(x,y,z) = (expression)(x,y,z) - c = 0.

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It's standard to do this.

honest idol
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again, always this freakin part

quiet plume
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Try (equation 1) - (equation 2).

honest idol
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bruh what am i doing

honest idol
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i just realized

quiet plume
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It's not

honest idol
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howcome

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i always get stuck on this part

quiet plume
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You have variables multiplied together.

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It's not a system of linear equations

honest idol
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yeah youre right

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the thing is every time we solve these its like we do something random every time

quiet plume
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It's not random. You have to spot things that you can cancel.

honest idol
quiet plume
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You can do whatever you would do to solve equations in general, there just isn't a cookie cutter way to do it like for linear equations.

honest idol
quiet plume
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From here you could've multiplied through by lambda l - 4

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This would give you a nice relation between w and l

honest idol
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all this is cuz of the overthinking

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test is in like 30 minutes so ill just lock on off of what i know

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@quiet plume thank you very much for your help

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i really appreciate it

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@quiet plume one last thing tho you said we dont care about lamda in these problems right

quiet plume
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We don't care about the particular value of lambda, no

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It does have a meaning, but for the purposes of optimization it's not relevant.

honest idol
quiet plume
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No, you can still use it.

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All I mean is you don't have to find its value

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Like you do for x,y,z.

honest idol
quiet plume
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It doesn't change anything.

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You could solve for x,y and lambda and then get z from one of the equations

honest idol
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i see

safe radishBOT
#

@honest idol Has your question been resolved?

safe radishBOT
#
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lone shuttle
#

Hey there, I'm trying to prove that if a topological space X is compact and Hausdorff, then X is normal (T4). The professors hint was to recall the proof for compact subspaces of Hausdorff spaces being closed and applying twice (once for each closed set), which i included below, but I really don't see how to do it. I'd really appreciate a further hint or something to guide me in the right direction :)

lone shuttle
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(I know this is a fairly standard result in general topology and that proofs exist out there but I feel like I miss out on a big part of the learning process by just finding the proof online)

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Let $K\subseteq X$ be compact, $X$ Hausdorff. Let $x \in X\setminus K$. $\forall y\in K$, by Hausdorffness, $\exists$ open $V_y \ni y, U_y \ni x$ s.t. $V_y \cap U_y = \emptyset$. Then ${V_y}{y\in K}$ is an open cover of $K$, hence $\exists$ finite subcover ${V{y_1}, ..., V_{y_k}}$. Then $U \coloneq \bigcap_{i=1}^k U_{y_i}$ is disjoint from $\bigcup_{i=1}^k V_{y_i} \supseteq K$, so $U\cap K =\emptyset$, i.e. $U \subseteq X\setminus K$, so $X\setminus K$ is open QED.

flat frigateBOT
safe radishBOT
#

@lone shuttle Has your question been resolved?

quiet plume
#

Take any two disjoint closed subsets A,B of X.
They're both compact as closed subsets of compact spaces are compact.
Iirc the idea is you can parameterize open covers of B in terms of each point of A using Hausdorfness (like in the proof you sent kinda) which also gives you an associated open cover of A. You should be able to get something nice if you tinker with those a bit.

lone shuttle
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maybe I just need to approach the problem with a better rested brain, ive always found point space topology to be a difficult subject

quiet plume
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Essentially, you should find a way to construct, for each element of A, an open neighbourhood of it and an open cover of B which doesn't intersect this open neighbourhood of A. Then you could string those along A and do more stuff to make sure everything is nice and disjoint.

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But yes, rest helps a lot!

lone shuttle
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just curious

quiet plume
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Hmm I’m doing masters atm but mostly differential geometry / algebraic topology type stuff

lone shuttle
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is there any diff geo textbooks you'd recommend? I'm taking a class on it this semester and my prof is so disorganized

quiet plume
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I think the standard one is Do Carmo’s diff geometry of curves and surfaces

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I think he explains relatively well and the first 3 or 4 chapters cover pretty much what one would see in a first course in differential geometry I reckon

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There’s Ted Shifrin’s notes online as well which may provide outside perspective

lone shuttle
# quiet plume Hmm I’m doing masters atm but mostly differential geometry / algebraic topology ...

I think I understand now, is the general idea to basically fix an element $x \in A$, and then for each $y\in B$, you get (similar to the proof above) some $U_y \ni x, V_y \ni y$ disjoint. You then get an open cover of B by ${V_y}{y\in B}$, you use compactness for a finite subcover ${V{y_1}, ..., V_{y_k}}$, then you set $\mathcal C\coloneq {U_{y_i} : 1\le i\le k_y}$, and repeat this $\forall x\in A$ to get a cover $\mathcal C \coloneq {U \in \mathcal{C}_X : x\in A}$, and you can then play around with it pretty easily to show its disjoint from B?

flat frigateBOT
quiet plume
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Yes, that’s pretty much the main point of the proof.

lone shuttle
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alright perfect I think I can do that now! thank u so much I really appreciate your help :)

quiet plume
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Of course

lone shuttle
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thanks again for the advice!!

quiet plume
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Yes that is true I found that as well reading it. Again Shifrin is pretty good and I think videos from, say, the bright side of mathematics, explain more obscure stuff nicely

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Happy learning!

lone shuttle
#

.close

safe radishBOT
#
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safe radishBOT
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rigid hemlock
safe radishBOT
clever tinsel
#

do you have an actual question?

safe radishBOT
#

@rigid hemlock Has your question been resolved?

safe radishBOT
#
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subtle crown
#

I need help with Excel, if anybody is familiar with the Goal Seek tool

subtle crown
#

B16 is my formula cell, F9 is my variable cell (y)

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I don't know why it isn't solving for y, so if anyone has some insight, I'd appreciate it.

#

.close

safe radishBOT
#
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safe radishBOT
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crude light
#

Hi guys could someone help me please, I think this is a binomial question but i dont use the formula i use a table

crude light
#

is this the correct layout, as in did i split it correctly

safe radishBOT
#

@crude light Has your question been resolved?

crude light
#

.close

safe radishBOT
#
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safe radishBOT
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dapper grail
#

https://claude.ai/share/62f8dac0-2d52-4470-8bc4-99bf3f9a3e02 Can someone explain me this Errichto iterative method for Chinese remainder thoerem? I haven't dropped the link of the video as some people may not like to watch a video just to explain a concept therefore they can read the claude explanation using this given link.

Claude

Shared via Claude, an AI assistant from Anthropic

buoyant shadow
#

I can't open the link

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i found the video, which part confused you?

dapper grail
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Actually i am on starting, I am not able to understand the starting part

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so i don't have any idea if i will be able to understand the rest or not

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https://youtu.be/EHDEvFuYPRQ?si=BYPmHCVfJ-jkAtVY here is the video i am refering to

A simple method for Chinese Remainder Theorem (solving system of congruences), without any modular inverse. Here's my code for Advent of Code day 13 https://github.com/Errichto/youtube/blob/master/AOC-2020/13-search/shuttle2.cpp

0:00 Example 1
2:02 In General
2:56 LCM
4:05 Big Example
7:31 Extra Understanding

Subscribe for more educational vid...

▶ Play video
vague phoenix
#

o this not working

vague phoenix
#

!1c

dapper grail
#

?

vague phoenix
#

ye

dapper grail
#

both have diffrent questions

#

well

vague phoenix
#

ask 1 at a time

dapper grail
#

ok

vague phoenix
#

type .close pls

dapper grail
#

done

dapper grail
buoyant shadow
#

it's like you're at the bus stop, and you just look at buses, and there's 3 lines, one arrives every 4 minutes, then there's another that arrives every 6 minutes, and there's a 5 minute bus
and there's not enough space for all three to fit, so you really want to stay and see what they will do

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3,5, 2 is when the next bus arrives

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you jut trial and error to find how long to wait

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until they all arrive at the same moment

dapper grail
#

Lemme read

buoyant shadow
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it's not chinese remainder theorem, it's too different, but people don't have different names for these problems for some reasion

dapper grail
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So it doesn't matter to me. If I am getting the answer

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🙂

dapper grail
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Alright

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But how will I find that?

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According to what i understand after watching some part of video

buoyant shadow
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you solve it for subsets

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first bus only, then first 2, then first three

dapper grail
#

Lemme explain

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What I have understood

dapper grail
buoyant shadow
#

yeah

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if there's 7 buses you do 7 sub steps, where you increase the step

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it's bruteforce that gets faster and faster

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wikipedia says you could optimize it if you change the order from big mod to small, that sounds right

dapper grail
#

Let,

x = a1 (mod m1)
x = a2 (mod m2)
x = a3 (mod m3)

Then,
x = m1 × k + a1

And also,
x = a2 × q + a2

Putting equation 1 into eq 2 -

m1 × k + a1 = a2 × q + a2

#

Hey wait, what am I doing? 💀

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I think it is not what he is doing

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In the video

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Did I mixed up two idea? Maybe 🤔

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Because I was studying diphontine equation as well

nimble wyvern
#

<@&268886789983436800>

dapper grail
#

Was gonna do it too

buoyant shadow
#
from math import lcm
buses = (4,3),(6,5),(5,2)
time = 0
step = 1
for m, r in buses:
   while time % m != r:
      time += step
   step = lcm(step, m)
#

that's all

dapper grail
#

I know C/C++ but not able to understand this code 🤔

#

By the way phone is about to die

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Will be coming back in half an hour.

buoyant shadow
#
mod = [4,6,5]
remainder = [3,5,2]
time = 0
step = 1
for(i=0, i < 3, i++) {
   while (time % mod[i] != remainder[i])
      time += step
   step = lcm(step, m)
}
#

more c less hiss

dapper grail
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What is time and step variable?

buoyant shadow
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integers?

dapper grail
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Ah yes

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Time = 0

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And step = 1

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What are these integers type variables

buoyant shadow
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no, that makes a tuple

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a tuple is a list without append method

silver current
#

I see

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I know

dapper grail
dapper grail
buoyant shadow
#

it's python things, sorry for spamming the channel

dapper grail
#

I think we shouldn't jump into coding before I understand general maths

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😅

#

The method in that video is not that complex

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I just need someone who can explain me what he is doing

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Basically

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I can explain the part I understand

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To see if I am right or wrong

safe radishBOT
#

@dapper grail Has your question been resolved?

clever tinsel
#

that's not the correct ping, just for your information. you pinged a user.

dapper grail
#

<@&286206848099549185>

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I hope it's right now

clever tinsel
#

that's the right ping.

safe radishBOT
#

@dapper grail Has your question been resolved?

dapper grail
#

Why is there no single helper to help me blobcry

safe radishBOT
#

@dapper grail Has your question been resolved?

dapper grail
#

Why is no one helping me

#

?

#

Have I asked a very bad question?

zenith maple
dapper grail
#

Lemme tag

dapper grail
zenith maple
#

@dapper grail are you atleast familiar with Euclid's division lemma

dapper grail
zenith maple
#

So in the video the focus is to find the set of numbers that give certain reminders under the given modulos

dapper grail
#

Ok

#

I understand this much atleast

zenith maple
# dapper grail Modulo yes

So you should be familiar with the idea that if a = b (mod c) a can be b + nc where n is any whole number

dapper grail
#

Ah basically this is the algebraical form of the equation of modular arithmetic

zenith maple
#

So for say two modular equations a = b (mod c) and a = p (mod q) we just need to find the first nc+b for which we get p under mod q

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Then to get the full set we need to keep on adding the least number that is 0 under mod c and mod q

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Which is the LCM

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Now if more equations are there repeat the steps where we need to find the least n(LCM) + the first nc+b (that is p under mod q)

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The guy in the video just focuses on how the remainders appear to get the needed value then to find the number corresponding to it he multiplies the LCM with the number of remainders till the needed one (since you have to add the LCM that many times to get the wanted number)

zenith maple
dapper grail
#

Lemme read

#

It's like -

#

Let,

x = a1 (mod m1)
x = a2 (mod m2)
x = a3 (mod m3)

Then,
x = m1 × k + a1

And also,
x = a2 × q + a2

Putting equation 1 into eq 2 -

m1 × k + a1 = a2 × q + a2


Then what do we do further?

dapper grail
#

.close

safe radishBOT
#
Channel closed

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Use .reopen if this was a mistake.

safe radishBOT
#
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fathom dock
#

Question 59

safe radishBOT
fathom dock
#

I figured out sin and cos, and i tried to use sin/cos to find tan but I can’t figure out where I went wrong

#

(Sqrt(6)-sqrt(2))/(sqrt(6)+sqrt(2))

midnight cypress
#

which exercise is this for

fathom dock
#

59

midnight cypress
#

Yeah you're right

#

as in your answer is right

fathom dock
#

Alr

#

So its just the solving part that’s wrong

midnight cypress
#

why do you think you're going wrong catthink

fathom dock
#

Well the equation i got after solving for tan is wrong

fathom dock
midnight cypress
#

ah

fathom dock
#

Multiplied the equation by the inverse of the denominator

midnight cypress
#

yeah you're making a mistake while rationalizing

fathom dock
#

I got (6-sqrt(12)-sqrt(12)+2)/4

midnight cypress
#

hmm

#

2-sqrt3

#

that's correct tho

stoic torrent
#

lmao

fathom dock
midnight cypress
#

yes

fathom dock
#

Then 4-sqrt(12)/2

midnight cypress
#

yes

fathom dock
#

The answer in the key is 2-sqrt(3)

midnight cypress
#

you can simplify this further

fathom dock
#

Oh you can?

midnight cypress
#

sqrt(12)=sqrt(4*3)

#

do you see it

fathom dock
#

Ohhh

#

I see it

#

Ah

midnight cypress
#

yep

fathom dock
#

I forgot you could do that

#

Lmao

midnight cypress
#

happens with the best of us 🙏

fathom dock
#

Thanks

midnight cypress
#

np!

fathom dock
#

Number 36

#

This one i genuinely just dont know where to start

midnight cypress
#

this one you can do in a lot of ways

fathom dock
#

Or wait

#

Mb

#

Its 35

midnight cypress
#

oh okay

#

yeah this one too

#

let's begin with the rhs

drowsy lake
midnight cypress
#

what's your first instinct seeing the big expression in cosx

fathom dock
#

Expand it

midnight cypress
#

no!

fathom dock
#

Oh

midnight cypress
#

your first instinct should be to take the terms common outside

fathom dock
#

Oh wait your going from right to left

#

I see

#

Thats smart

midnight cypress
#

ah

midnight cypress
fathom dock
#

Yeah ig

midnight cypress
fathom dock
#

Yesyes

#

1-2cos^2x is cos

#

Cos2x

#

I think

midnight cypress
#

you're left with cos^2x(1-2cos^2x+cos^4x)sinx

#

the term in the bracket

#

any algebraic identity u remember?

fathom dock
#

Cos 2x

midnight cypress
# fathom dock Cos2x

you're not wrong here, its -cos2x btw, but that's not helping us in getting closer to something that looks like the RHS

#

2cos^2x-1=cos2x

midnight cypress
fathom dock
#

Its not coming back

midnight cypress
#

wdym

fathom dock
#

I dont remember the identity

midnight cypress
#

a^2-2ab+b^2

fathom dock
#

Ohh

#

I remember

midnight cypress
#

so u see how this is applied right

#

can you do this for me till here?

fathom dock
#

Wait hold on

midnight cypress
#

I think you'll be able to see the next step

fathom dock
midnight cypress
#

1-2cos^2x+cos^4x

#

let a=1, b=cos^2x

#

do u see it now

fathom dock
#

Sorry its just not clicking

midnight cypress
#

1-2*1*cos^2x+(cos^2x)^2
Now?

fathom dock
#

Oh alr that makes sense

midnight cypress
#

so this is just

#

(1 - cos^2x)^2

fathom dock
#

OHH

#

I see it now

fathom dock
midnight cypress
#

you need to learn your algebraic identities fr

fathom dock
#

Yeah

midnight cypress
#

there's another way

#

you begin with sin^5xcos^2x

#

and then you notice how the RHS has a lone sinx

#

so you take that out of sin^5xcos^2x

#

sinx(sin^4x*cos^2x)

#

now you see that

#

sin^4x=(sin^2x)^2

#

and from here you could do it

#

it's basically the opposite of what we did

fathom dock
#

Im trippin

#

So you got sinx((sin^2x)^2 * cos^2x)

midnight cypress
#

yep

#

when u see sin^2x what identity come to mind

#

or u can see that in RHS

#

all the other terms are in cos

#

so how do u convert sin^2x in terms of cosx

fathom dock
#

Wait give me like 2 mins

#

Bavk

#

Back

fathom dock
midnight cypress
#

you've learned sin^2x+cos^2x=1

#

right

fathom dock
#

Yeah

midnight cypress
#

(use that)

#

(do u see it?)

fathom dock
#

If there was like a 1-sin^2x i would get it

midnight cypress
#

hmmmmmm

#

don't u think u can manipulate sin^2x+cos^2x=1 to get it that way?

#

this identity is true always

fathom dock
#

Well you subtract sin^2x to get it that way

midnight cypress
#

yeah

fathom dock
#

What do i do with that

midnight cypress
#

well you can also notice that you can subtract cos^2x instead

fathom dock
#

OHHHH

#

WAIT

#

I GET IT

#

sin^2x is 1-cos^2x

midnight cypress
#

correct

fathom dock
#

Idk why that took me so long

midnight cypress
#

it's okay

fathom dock
#

So then you got sinx((1-cos^2x)^2 * cos^2x)

#

1-2cos^2x+cos^4x

#

Times cos^2x is sinx(cos^2x-2cos^4x+cos^6x)

#

Yay

#

Thanks

midnight cypress
#

np!!

safe radishBOT
#

@fathom dock Has your question been resolved?

safe radishBOT
#
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void locust
#

Guys can someone confirm if this is correct

void locust
#

<@&286206848099549185>

stoic torrent
#

,w 300102 * pi /360

stoic torrent
#

K part a is correct

#

,w pi ( 100) / 6

stoic torrent
#

Dont forget the units!!

safe radishBOT
#

@void locust Has your question been resolved?

void locust
safe radishBOT
#
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stoic torrent
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normal moss
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solar inlet
safe radishBOT
solar inlet
#

how do i find the range

mighty cairn
#

Let f(x) is equal to y

#

Then find x in terms of y

frozen veldt
#

Beyond that, the function is strictly decreasing

#

however it will never equal 0 or be a negative number

#

but it will be arbitrarily close to 0

#

You can show that in more mathematical detail if you're interested

#

but that's the intuition

solar inlet
#

but like why do we include 0 in the function to get 3 cuz like the x values RE GREATER than 0 so should we not plug in 1

frozen veldt
#

That's an excellent question

#

The trouble is that 1 is already overshooting by a lot

#

because it would be better to start from 0.1, or 0.01, or 0.001, or 0.0001, or something like that

#

but if we play that game we'll always miss out on possible values

#

So it's a better idea to start from 0, then just exclude 3 from the range because x=0 is not actually allowed, and reason that anything slightly smaller than 3 must be doable

solar inlet
#

oh

frozen veldt
#

As an exercise you can try showing that there is an x for which f(x)=2.99 even though there is no x for which f(x) = 3

solar inlet
#

okay so what if it was x>=1

#

then what would the range be

frozen veldt
#

In that case you can plug in x=1 to get 1

#

and this time you don't have to exclude it from the range

solar inlet
#

oh

frozen veldt
#

then you can again reason that the function is strictly decreasing etc.

solar inlet
#

i see

#

tysm gng

frozen veldt
#

no worries ^^

solar inlet
#

wait

#

one last qs

#

@frozen veldt

frozen veldt
#

sure

solar inlet
#

what if it was

#

x>2

#

we plug in 2

#

right?

#

and exclude it from range

frozen veldt
#

that works

solar inlet
#

alr bet

frozen veldt
#

well done

safe radishBOT
#

@solar inlet Has your question been resolved?

#
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delicate radish
#

i am back with the work

safe radishBOT
delicate radish
#

its saying the second coord for both version are incorrect

mortal sandal
#

,calc 1/sqrt(17)

flat frigateBOT
#

Result:

0.24253562503633
delicate radish
#

il try and put all that in and see

mortal sandal
#

you can try using more digits, it could be that

delicate radish
mortal sandal
#

strange

#

its off by about 0.2%

delicate radish
#

ts webwork

#

.close

safe radishBOT
#
Channel closed

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mortal sandal
#

,calc 1/sqrt(5)

flat frigateBOT
#

Result:

0.44721359549996
safe radishBOT
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white pebble
#

yo guys,
if i wanna get the inflection points of an function and the 3rd derivate is equal to 0, that doesnt necessarily means its no inflection point but what do i do then

white pebble
#

or what does it even means when its 0

tardy mango
# white pebble yo guys, if i wanna get the inflection points of an function and the 3rd derivat...

If the third derivative is zero at a point where $f''(x)=0$, then the test is inconclusive. You'd have to keep checking higher order derivatives until you find the first one that is not zero.
\begin{itemize}
\item If the first non-zero derivative is of odd order, then you have an inflection point.
\item If the first non-zero derivative is of even order, then you do not have an inflection point.
\end{itemize}
(Note that this only works under the usual smoothness assumptions.) \

Honestly, you're better off just doing sign analysis on $f''$.

flat frigateBOT
#

Civil Service Pigeon

white pebble
#

oh okay

#

thanks

tardy mango
safe radishBOT
#

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

white pebble
#

.close

safe radishBOT
#
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honest idol
#

hello, i need help setting up the objection function and the constraint function

safe radishBOT
#

@honest idol Has your question been resolved?

honest idol
#

i dont know where to start

#

thats the issue

#

<@&286206848099549185>

still stone
#

do you know what a lagrangian is?

#

or using lagrange multipliers?

honest idol
#

i understand how it works but not here

safe radishBOT
#
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plucky elk
honest idol
#

.reopen

safe radishBOT
plucky elk
#

Anytime you're given a fixed number for Lagrange multiplier problems, that's probably your constraint. Write down two equations for volume and surface area first

winter whale
#

Waaaaarmaaaaaaan

honest idol
#

idk whats gonna be different here

honest idol
#

have we talked before

#

dude why am i lowkey known all over discord

plucky elk
honest idol
#

i wouldnt say so

plucky elk
#

Whatever assumptions you made in 4.7 apply here too

honest idol
#

if then so whats the point of it having no lid i dont get it

plucky elk
plucky elk
honest idol
plucky elk
honest idol
#

oh

#

yeah

#

i thought you were lurking cu yestderday i was asking questions

plucky elk
#

"same problem from 4.7"

still stone
#

like

#

uhh

#

imagine a cup

#

there is a certain volume of water that goes in it, will it matter how much water it can hold if it has a lid or not?

#

what matter are the dimensions

honest idol
still stone
#

now so the volume will be length x breadth x height = 4ft^2 like usual

honest idol
#

whats confusing to me is the idea of how this can show us the gradient of the level curve and that of the objective curve

#

like

still stone
#

?

plucky elk
#

That has nothing to do with volume and surface area

still stone
#

just focus on your functions first

plucky elk
#

Maybe you should learn to focus on basics first

honest idol
still stone
#

yes but our main goal is to find the functions to apply lagrange multipliers onto

plucky elk
#

Read the first two formulas and make sure you understand them before learning Lagrange multipliers

plucky elk
plucky elk
#

?

honest idol
#

i have no idea dude

#

like im actually confused

#

theyre saying they want the least amount of cardboard possible

plucky elk
honest idol
#

such that the entire volume = 4

honest idol
#

but not in terms of

#

what we need to optimize

#

and what the constraint is

plucky elk
plucky elk
plucky elk
honest idol
honest idol
plucky elk
plucky elk
plucky elk
plucky elk
plucky elk
# honest idol

You're ignoring the "without a lid" part of the question

honest idol
plucky elk
plucky elk
honest idol
#

so are we subtracting an area of one side?

#

which is the top

plucky elk
#

Right

honest idol
plucky elk
#

I mean you should simplify but yes that's right

plucky elk
#

Yea now and only now can you start thinking about calculus

honest idol
#

okay

plucky elk
#

If you don't know your basic volumes, surface areas, etc. you should not be thinking about calculus

honest idol
#

i do know

honest idol
#

yeah thats one of the things that are confusing me

plucky elk
#

Yea that had nothing to do with volume or surface area of a box

honest idol
#

we want critical points restricted by a level curve of some other function

#

right

plucky elk
#

Do you know what those words mean

honest idol
#

such that the gradient vector of the level curve at some constant is a scalar multiple of the gradient of the objective function at that same point

honest idol
#

but not how they look like here

plucky elk
#

What's the level curve in this question then

honest idol
#

i have no idea

#

thats the thing

#

but i know we need one

#

im gonna assume its the contraint fomrula since all our level curves are considered the constraint

#

but i dont understand why thats the case

plucky elk
# honest idol

Your choice of f and g are fine here. Do you know what equation you need next from the words you just said

honest idol
#

because to begin with i dont even know how the concept of critical points on g = c applies here

plucky elk
#

Maybe since you can't come up with an equation, you should just memorize the equation

#

$\grad f(x, y, z) = \lambda \grad g(x, y, z)$

flat frigateBOT
#

pi_day

honest idol
#

which one is the level curve

plucky elk
#

Do more problems and see what works

honest idol
#

but theres gotta be properties that renders one a constraint formula that we should be able to identify right

plucky elk
#

In reality, it doesn't matter which one is f and g. Solving

grad f = lambda * grad g

is the same as solving

grad g = (1/lambda) grad f

#

Since lambda doesn't matter, and only x, y, z, your answer should be the same

plucky elk
# honest idol but theres gotta be properties that renders one a constraint formula that we sho...

You should just memorize the blue box here
https://tutorial.math.lamar.edu/classes/calciii/lagrangemultipliers.aspx

And do the calculations in example 1 since you need to read a lot of examples. They will be nearly identical to your problem.

safe radishBOT
#

@honest idol Has your question been resolved?

honest idol
#

So I can scale whichever vector right

#

Like either one can be the scalar multiple

plucky elk
honest idol
#

Thanks for your help tho

honest idol
#

Like the vectors are parallel

#

So you can scale either one to get the other

#

Right

plucky elk
#

Do one problem completely before moving on

plucky elk
#

And

plucky elk
safe radishBOT
#

@honest idol Has your question been resolved?

safe radishBOT
#
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solemn glade
#

any insight on how to solve since i don't find any option related to the outcome of the equation i worked

pine wind
#

what did you try?

safe radishBOT
solemn glade
hasty wagon
vague phoenix
solemn glade
hasty wagon
solemn glade
hasty wagon
hasty wagon
solemn glade
near sky
# solemn glade

hm.. i would say it should have been $\sqrt{1- a^2} = |\cos x|$ but they do not seem to consider that

flat frigateBOT
#

professor paradox

hasty wagon
#

like $\frac1{\sin x}+\frac1{\cos x}=\frac{?+?}{\sin x \cos x}$

flat frigateBOT
#

Biscuity

hasty wagon
solemn glade
hasty wagon
#

yea

#

now we have sin(x) + cos(x) as the numerator

#

we tryna divide the numerator by sin(x)

#

we can get 1 + cot(x)

#

all good till here?

solemn glade
#

yeah

hasty wagon
#

after that we just plug back in to get the answer

solemn glade
#

i think i get it

#

how to not get lost while doing htese kind of questions though

hasty wagon
#

finally check to see if which choice is good to transform into

#

e..g. i look at E, and see there's (sin x cos x) in the denominator

#

then I'll aim for that option E

#

Hope that helps!

solemn glade
#

thanks

#

!close

#

!stop

#

eh how to

hasty wagon
#

it's .close

solemn glade
#

.close

safe radishBOT
#
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safe radishBOT
#
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zenith creek
safe radishBOT
zenith creek
#

hello i had this question and i just wanted to know how it should be approached first and what the idea is here?

upbeat swan
#

do you know how to do polynomial long division?

bitter fossil
#

Guys what is 1 plus 1 equal

upbeat swan
#

um idk 2?

vague phoenix
upbeat swan
#

well then do that

#

and see what you get

bitter fossil
#

Good boy correct

upbeat swan
#

thank you

bitter fossil
#

What is sin

vague phoenix
upbeat swan
#

its when you do a bad thing

zenith creek
whole hill
upbeat swan
#

i mean

#

after long division its preety simple

fathom jewel
zenith creek
#

let me give it a try

upbeat swan
#

because long division allows you to identify the asymptote

velvet lodge
#

asserting dominance

upbeat swan
#

yeah well the green ones have dominion over the help channels

zenith creek
upbeat swan
#

just treat it like a nuber

#

number

zenith creek
#

hm

velvet lodge
#

or an explanation

upbeat swan
#

instead of a

#

imagine that its a 2

#

or a 67

#

anything

#

and then just carry that 67 over

zenith creek
velvet lodge
#

goodluck

upbeat swan
#

cheers

vague phoenix
#

Didn't help and send random stuffs

velvet lodge
velvet lodge
upbeat swan
#

🤣

zenith creek
#

right now the asymptote i got is 2x+(a+2) so im guessing i should equalize the (a+2) and the -4?

velvet lodge
#

@vague phoenix lets just stop the beef alright

velvet lodge
#

and all be friends

#

❤️

zenith creek
#

and its equal to -6

covert shell
#

Yoo

upbeat swan
#

yeah

zenith creek
upbeat swan
#

-6 should be right

#

yes

zenith creek
#

yeah thanks mate

upbeat swan
#

no worries

upbeat swan
#

cute

upbeat swan
zenith creek
#

how do i unoccupy the channel?

upbeat swan
#

.close

covert shell
#

Am new here

zenith creek
#

.close

upbeat swan
#

cool

safe radishBOT
#
Channel closed

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velvet lodge
upbeat swan
velvet lodge
#

@vague phoenix do you forgive me bro

upbeat swan
velvet lodge
#

you're a very smart guy

#

i apologise for interrupting you earlier

covert shell
#

I want you guys to asses me I like math but am bad at it

velvet lodge
patent citrus
#

hes chill

covert shell
#

Am junior at highschool

upbeat swan
covert shell
#

I don't have any question right now

velvet lodge
# patent citrus how did you end up getting a beef w him lol

pretty much i asked a question about which maths to focus on in relation to quantitative finance, he told me i was asking "off topic questions" i tried explaining that it wasnt and it was directly related to maths, he had a go at me and called me a clown, then 3 other dudes actually came in and answered my questions

#

fun times

velvet lodge
#

so hopefully everything will be well and good

velvet lodge
#

just say the age 😭

glass egret
velvet lodge
#

@covert shell what maths u doing atm

covert shell
velvet lodge
#

you would just be called yr 11 here

covert shell
#

Nothing

velvet lodge
#

or u just

#

not doing maths

#

at all

covert shell
velvet lodge
#

?

#

did you get held back

covert shell
#

No I started 1 yr later

velvet lodge
#

are you taking maths

#

in hs

#

?

covert shell
#

Ofc it's obligatory 😭

#

If there was a possibility I wouldn't learn it

upbeat swan
#

L

#

math is everything

safe radishBOT
#
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covert shell
safe radishBOT
covert shell
#

am open

upbeat swan
#

hm

#

this channel is for specific questions

#

if you wanna talk about it

#

we can go to the discussion channels

covert shell
#

Ok

upbeat swan
#

so if you dont have a question

#

you can type .close

normal moss
#

.close

safe radishBOT
#
Channel closed

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#
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safe radishBOT
#

Please don't occupy multiple help channels.

upbeat swan
#

interesting

safe radishBOT
#
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normal moss
safe radishBOT
#
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terse burrow
#

Hi. This might sound silly. I’m a secondary school maths teacher and I’m marking an assessment I gave to one of my classes. This was one of the questions. I attempted the question in two different ways and got two different answers. Method one is the correct way, but I don’t know where I have gone wrong in method 2.

vague phoenix
#

Strange, they looks both valid.

terse burrow
#

<@&286206848099549185>

stuck basalt
#

interesting

vague phoenix
terse burrow
#

This is the mark scheme for the question

#

The gaps between 12.7 and 3.2 should be +

vague phoenix
#

Ah I see why!

#

For the second way you found, if a = 14.8, then R = 54.8

#

This contradicts with the given information of the question, where PQ=20*sin(R)

#

Even though your second step is in fact correct, but if plug back into the original question information, it did not satisfy the given conditions.

urban crown
#

I'm finding inconsistencies in the triangle

vague phoenix
#

You can test for R such that $PQ=20sin(PRQ)$ such that $PQ=15.9$

flat frigateBOT
vague phoenix
#

Does this make senses @terse burrow ?

terse burrow
#

Yes

#

What inconsistencies do you see by the way?

urban crown
#

I don't think it's a possible triangle, which is why the answer for a cannot be consistent regardless (but I could be wrong)

urban crown
#

When a = 12.655 deg, then <QSR = 180-90-a = 77.345
Hence, <PSR should = 180 - <QSR = 102.655
Using sine law on the upper (non right) triangle, sin(102.655) / 20 should equal sin(40) / 12.7 I believe?

#

But I'm getting 0.0488 ≠ 0.0506

terse burrow
#

I see that now. Thank you for your help.

#

.close

safe radishBOT
#
Channel closed

Closed by @terse burrow

Use .reopen if this was a mistake.

vague phoenix
#

No problem, good luck in teaching!

safe radishBOT
#
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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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scarlet storm
#

can anyone help me understand logarithms ?

pine wind
#

do you have a problem you were stuck on?

split kayak
#

Any particular question?

scarlet storm
#

i just came into 11th and wanted to discover it as my first chapter

vague phoenix
#

Have you taken a look at your textbook?

pine wind
scarlet storm
#

i have applied mathematics

#

i dont quite understand what logs are for ? are they for finding a power ?

split kayak
#

Well, just to start, you should know that the main purpose for logarithms to exist (as they were first created in ~1615) is that they have the main property of transforming multiplication into addition.

scarlet storm
#

OooooO

#

How so ?

split kayak
#

Since addition is a far easier operation, they created tables so you can find the logarithm of the numbers you want to multiply, and the number you get from it

#

This is because the logs satisfy the property

scarlet storm
#

like that a^m * a ^n = a^m+n ??

split kayak
#

log(a) + log(b) = log(ab)

scarlet storm
#

ohhh

#

that's pretty gooood

split kayak
#

So, for example

scarlet storm
#

uh huh

split kayak
#

Say we work in logarithm base 10 (we will see later what that means)
and you want to compute (easily)
134 * 211

#

Well, by property of logarithms we have that

scarlet storm
#

oh is that so, without multiplying ?

split kayak
#

log(134 * 211) = log(134) + log(211)

scarlet storm
#

damnnn

split kayak
#

you can then compute the sum of logs.

scarlet storm
#

ohhhhh so i would require to look into the table ?

scarlet storm
split kayak
#

log(134) + log(211)
2.1271... + 2.3243... = ~4.45138

scarlet storm
#

welp thanks anyways !!

#

uhhh wats that 😭

split kayak
#

mb, you can see above what those numbers are

#

its the numerical value for log 134 and log 211

scarlet storm
split kayak
#

Then you look up what number corresponds to ~4.45138

scarlet storm
split kayak
#

and you would know that the multiplication = 28274

#

just by looking at 3 values on a table

scarlet storm
stuck basalt
#

here’s some intuition you should build

$\log_{x} y = z$
just means
$x^z = y$

so when you are given something like

solve $\log_{2} (4) = x$

that just means

“what number $x$ can i raise 2 to in order to get 4?

scarlet storm
#

thank you for your help man !! really appreciate it