#help-33

1 messages · Page 104 of 1

ebon depot
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On b) it says:

if $\lambda^4 = 1$ then $v_1 = [1, \lambda, \lambda^2, \lambda^4]^T$ Which should hold true since one of the eigenvalues is 1 and the corresponding eigenvector is $[1,1,1,1]^T$

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Am i thinking correct?

elfin berryBOT
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Merineth

ebon depot
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marsh citrusBOT
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urban bobcat
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can someone help me solve this i have already solved a. "Let F : R^4 → R^4 cyclically map the basis vectors e1F→ e4F→ e3F→ e2F→ e1.
(a) Derive F's mapping matrix A, such that F(x) = Ax. Show that A4 = I4 and that AT = A−1 = A3.
(b) Show that if λ^4 = 1, then λ is an eigenvalue of A with associated eigenvector (1, λ, λ^2, λ^4)T.
(c) Brilliant and diagonalize: Find a diagonal matrix D and an invertible P such that A = P DP ^−1

marsh citrusBOT
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@urban bobcat Has your question been resolved?

urban bobcat
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Can I use the formula A*e = lambda *e?

marsh citrusBOT
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@urban bobcat Has your question been resolved?

marsh citrusBOT
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@urban bobcat Has your question been resolved?

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slow holly
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How would I approach this? I’ve already tried reversing the summation and converting it all to exponential functions but neither of those seem to lead anywhere

slow holly
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Dn is the dirichlet kernel btw

upbeat sable
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Looks like they multiplied the numerator and denominator by sin(x/2) and used the product to sum formula

slow holly
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Hmmm ill try that

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I need to look at the product to sum formulas I guess because all I’ve been doing is converting to exponents, doing some algebra, and converting back lol

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I’ll keep the channel open for now in case I fail miserably

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Wait this is a telescoping series now

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Thanks!!

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upbeat sable
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Yes

marsh citrusBOT
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lilac scaffold
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would anyone like to verify my work?

marsh citrusBOT
lilac scaffold
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this is the original question

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part b

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I'm adding 2 vectors and using cosine and sine law to find the magnitude and bearing

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I believe my cosine law is 100% correct, I just want someone to double check the sine law

marsh citrusBOT
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@lilac scaffold Has your question been resolved?

lilac scaffold
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<@&286206848099549185>

marsh citrusBOT
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@lilac scaffold Has your question been resolved?

slim spire
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I think you used the wrong numbers for the sine law, it should always be the angle over the side directly opposite of it

lilac scaffold
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wdym

slim spire
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which sin(B)/7 isn't

lilac scaffold
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oh thats my bad

slim spire
lilac scaffold
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it should be sin(b)/2 right?

slim spire
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if you're trying to find that angle on the left yea

lilac scaffold
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yeah exactly

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cause when i find that interior angle, i can add the angle between the line a and 90 degrees

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then subtract it by 90 degrees

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and that would be the distance between 0 degrees and the dotted line

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ykwim?

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which should be 45.4

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...if i got evertything right

slim spire
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I get 20 degrees, let me check it with sine law

lilac scaffold
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ok

slim spire
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was this what you had?

lilac scaffold
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i got the answer in a decimal

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and no

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the top part is 2sin133

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which is the same as 2sin47 i believe but whatever

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either way there should be that 2 in front

slim spire
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oh I have the wrong angle mb

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uhh what numbers did you get for the sine law angle then the final answer?

lilac scaffold
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the sine law angle was about 14.6

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then considering theres 60 degrees above that, the final answer (the heading of the dotted line) should be 45.4

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...i think

slim spire
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I guess it's the cosine law magnitude giving the discrepancy hmm

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maybe a calculator typo?

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ok yea you have to extend this square root over the whole thing to get 8.49

lilac scaffold
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am I supposed to get 8.49?

lilac scaffold
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sorry thats also a mistake

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its supposed to be over the whole thing

slim spire
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yea if you fix the square root it gets 8.49 and that'll fix everything

lilac scaffold
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oh shit wait

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cos133 is different than cos47

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i originally used cos47 in my calculation

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and theyre not the same at all

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uh ohhh

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okay gimme a couple minutes let me redo it

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okay it says the interior angle is 9.9

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that seems quite small..

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thats possible though right?

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like it doesnt seem unrealistic?

slim spire
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9.9 is right

lilac scaffold
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and i just did it for the other angle

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itll add up to 180

slim spire
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probably because the side length 2 is so small

lilac scaffold
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or like.. 179.9

lilac scaffold
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my drawing isnt quite to scale loll

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okay i guess thats the end of it

slim spire
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just to check what do you get after 9.9? for the final angle bearing

lilac scaffold
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50.1

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so

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therefore statement

slim spire
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oh 50.1 is off let me draw it

lilac scaffold
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a+b-> is 8.5m/s [050.1 degrees]

lilac scaffold
slim spire
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like this

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and you want the angle under the red

lilac scaffold
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yeah

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but nono

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hold on

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oooh ya i even did that wrong

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jeez

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it should be 30 - 9.9 right?

slim spire
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right

lilac scaffold
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i was doing 60-9.9 like from the top

slim spire
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the other way should've worked but there's a lot of minus signs to mess up

lilac scaffold
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hm

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okok

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so

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therefore statement

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a+b-> is 8.5m/s [020.1 degrees]

slim spire
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yup I confirm

lilac scaffold
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awesome

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jeez i wouldve messed that up so badly

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thanks a lot

slim spire
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👍 np

lilac scaffold
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situations like these helps me understand how important it is to check eevery possible mistake

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🙏

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hexed pilot
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Really can't think of much, tried substituting some variables in hope but got nowhere

marsh citrusBOT
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vestal mist
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i tried using ptolemies but now im stuck

marsh citrusBOT
vestal mist
marsh citrusBOT
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@vestal mist Has your question been resolved?

vestal mist
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anyoneeeee

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<@&286206848099549185>

marsh citrusBOT
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@vestal mist Has your question been resolved?

vestal mist
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Anyoneeee

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What

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vestal mist
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.reopen

marsh citrusBOT
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vestal mist
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You guys really hate geo

cobalt sentinel
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who doesnt

void elm
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I personally don't know any geometry, so I couldn't help if I wanted to

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not that I want to do geometry anyways lol

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I suppose you should just be patient and wait for someone

still temple
still temple
marsh citrusBOT
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@vestal mist Has your question been resolved?

vestal mist
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nooooooo

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open sentinel
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can some help me show that these are equal by hand?

open sentinel
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(1/3) k (k+1) (k+2) + (k+1) (k+2) = (1/3) (k+1) (k+2) (k+3)

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I put it into the computer and it told me there are equal but i cant figure out how to do it by hand

whole sleet
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~~Expand the left side
Expand the right side

You should get the same thing~~

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Actually nvm. Take the left side and common factor (k + 1)(k + 2)

open sentinel
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factored it out and got (1/3)(k+1)(k+2)(k+1)

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im not sure where the k+3 is coming from

whole sleet
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Watch out for that 1/3. You should have got:
(k + 1)(k + 2)(1/3 k + 1)

open sentinel
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okay I see

whole sleet
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If you then proceed to factor that 1/3 out, you will get the right side exactly

open sentinel
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okay thank you

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eternal meteor
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anyone how to approach this problem?

marsh citrusBOT
static quarry
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well first find the "orthogonal complement of the column space of (1,1)"

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which is a rather obtuse way of saying something much simpler in this case

eternal meteor
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right, how do I find an orthogonal complement of a vector

static quarry
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well in this case you're in 2 dimensional space

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so what is the dimension of the orthogonal complement of a vector?

eternal meteor
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wait, vector orthogonal to [1,1] is either [-1,1] or [1,-1] right?

static quarry
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sure

eternal meteor
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cool thnks

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that's neat

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and then project the 2 other vector onto [1,-1] right?

static quarry
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yep

eternal meteor
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aight thnks

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tall sun
marsh citrusBOT
tall sun
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the only limitation i see is like

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its not an actual graph or whatever

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what do they want??

haughty portal
tall sun
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oh my god

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hello again

haughty portal
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yeah lmao

tall sun
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how embarassing

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anyways-

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that makes this significantly easier

haughty portal
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yep

marsh citrusBOT
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normal knot
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Been studying for too long and officially braindead. I'm sure it's obvious, but I can't think.

Why would it be nonsensical or invalid to do:

P=P(1+r/e)^et

Yes, I know this is incorrect. I know that e represents continuous growth. I know I'm plugging e into the discrete compound interest formula. I'm just asking for clarification on specifically why we can't just say "e times over the course of a year," etc.

normal knot
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Like, if we were just some crazy bankers looking to have fun, and we just decided to get wonky and do interest with this formula (whenever the interest rate is supposed to be continuous), what would happen to the money?

cobalt sentinel
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,w eulers number

cobalt sentinel
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e is approximately 2.718

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meaning you'd compound 2.718 times a year

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which would work just like how youd compound 2 times a year

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or 4 times a year

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or 10 times a year

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if u want to compound continuously, use A(t) = P*e^(rt)

normal knot
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Why do we raise e to the rate? Maybe I need to sleep lol

cobalt sentinel
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im sure theres some proof of continuous compounding out there somewhere

fervent rampart
cobalt sentinel
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(1 + 1/x)^n as n to infty

normal knot
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Thanks folks, I'll take a look at that and maybe some proofs.

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Please don't occupy multiple help channels.

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slim brook
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I don’t know if I’m on the right track or if I did this correctly.

slim brook
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I’m so confused

calm harbor
calm harbor
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You’re not supposed to get x when solving for p

slim brook
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Idk how to approach the question

calm harbor
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I suggest you set f(x) = g(x)Q(x)+r(x)

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Q stands for quotient

slim brook
calm harbor
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yep

slim brook
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I did that and then I rearranged to isolate for p

calm harbor
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yes

slim brook
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Should I do the division statement for my long division or for the info in the question? I mean with -13 and stuff

calm harbor
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Just set every unknown coefficient about Q as a b c d

slim brook
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Oh ok

calm harbor
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Ping me when you’re still confused after trying

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sudden mauve
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where is (4)(24) coming from, since we are not given a function?

void elm
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base is 4, height is 24

sudden mauve
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why are we just ignoring the intgrals then?

void elm
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wdym

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the definite integral from 0 to 4 is just the area of a triangle

sudden mauve
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like youre not integrating anything youre just using the forumla for the area

sudden mauve
void elm
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It’s f(x) = 6x when 0 leq x leq 4, and f(x) = 24 when 4 leq x leq 8

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if you wish, you may integrate that as you like

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But you’ll see that you get the same result as just adding the areas of the triangle and rectangle components

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that’s why it’s far quicker (and probably preferable) to just use formulas for the area of a rectangle and triangle

sudden mauve
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ohhh i see

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thank you!!!!

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velvet sedge
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.close

potent token
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why is 0^0 equal to one? if i use the same argument for 0/0 being indeterminant (approaching negative infinity, positive infinity, and zero), 0^x equals zero for all x values up to 0₊, and on the right it equals 1/0^x, which is also undefined. meanwhile, x^0 always equals 1. is there something i'm misunderstanding?

desert dirge
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this is just one of those things
some will say its 1, some undefined, some 0, though usually either of the first two

saying its 1 is just from the definition that any number ^0 is 1

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its context dependent

potent token
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like i understand how it can be seen as indeterminate for calculus, but if we can just set 0^0 to be defined as 1 in some cases, why cant we do 0/0 = 1 because any number x/x = 1?

limber lintel
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Because you’re dividing by 0

desert dirge
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if x=0/0 then x*0=0, x could be anything for this to hold so x doesnt really have a defined value, thats perhaps an overly simplisitic look at it

marsh citrusBOT
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zenith knoll
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0/0 is undefined

potent token
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im not confused rn im just testing something out

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one moment

potent token
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okay wait

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this might be horribly wrong but

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is this a valid way to define 0^0?

desert dirge
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that works i suppose

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actually

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no

potent token
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it's not really rigorous since im multiplying by ln(0) and just setting it to zero

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that's the problem

desert dirge
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yeah its dodgy

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its more a definition than something to be proven

potent token
desert dirge
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definitions are just things we accept as true

potent token
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but i dont like that :(

desert dirge
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0^0 is defined differently based on the context

desert dirge
potent token
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welp

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foggy atlas
#

Which of these is a map/illustration (not sure what the correct term of it is in english) and why (not)?

z : IR → IR with z(x) = { ⌊x⌋ for x ≥ 5
−x + 9 for x ≤ 5}

w : IR → IR with w(x) = { 4x² for x ≥ 2
⌊9x − 3⌋ for x ≤ 2}

foggy atlas
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my approach is: both aren't maps because the in the definition area are values that are connected with values more than one time. If I put 5 in ⌊x⌋, I get 5. If I put 5 in −x + 9, I get 4. So 4 != 5

slim spire
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I agree, they're both not functions/maps because of the multivalued parts you said

foggy atlas
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and is this a function? f : IN → Z with f(x) = 3x/sin²(x)+4

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I would say it is again not a function

slim spire
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uhh how does you class define IN because everything is fine besides x=0

foggy atlas
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oh IN is like {1.....100000+}

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1,2,3,4,5

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all natural numbers from 1

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I thought that sin²(x) is (sin(x))² and then sin(x)

so 3x/sin(x)+4, when I put in 1 I get 3/0,017+4
3/4,017 = 0,74

and 0,74 is not a natural number

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but maybe I'm wrong

slim spire
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oh right makes sense, not a valid function

foggy atlas
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okok

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still temple
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Find any horizontal or vertical tangents to:

marsh citrusBOT
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@still temple Has your question been resolved?

still temple
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<@&286206848099549185>

still temple
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<@&286206848099549185>

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<@&286206848099549185>

marsh citrusBOT
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@still temple Has your question been resolved?

grave sequoia
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then take the derivative of each and equate to 0

grave sequoia
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what were you unsure about then

still temple
grave sequoia
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okay

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if you start with x

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you can multiply the expression for r by cos(theta)

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so 3(1 - cos(theta))(cos(theta))

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then you'll end up with an expression for x in terms of theta

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and if you take the derivative with respect to theta

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then equate that to zero

#

then you can solve for the angle at which the rate of change of x is zero

#

which would be a vertical tangent

#

then you can take the angle you get and substitute it back into the x = r * cos(theta)

#

and you should get an x = ___ line as your tangent

#

then you can do the same for y

marsh citrusBOT
#

@still temple Has your question been resolved?

marsh citrusBOT
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wary yew
#

Can you please check if the proof is correct

marsh citrusBOT
wary yew
#

Prove $(k,m)=1 \implies (m-k,m)= 1$\

Proof: Suppose $(m-k,m)=d \neq 1. \
d |(m-k)$ and $d|m
\implies d|m$ and $d|k$

but this contradicts (m,k)=1

elfin berryBOT
wary yew
#

i think i should add little more on how d|(m-k) implies d|m and d|k

#

Improved version, please check

marsh citrusBOT
#

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mint wind
marsh citrusBOT
#

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shadow thorn
#

Does this limit exist (as x approaches 0)?

charred pelican
#

yes

fathom ridge
#

does it?

shadow thorn
#

Because from both sides they approach 5

fathom ridge
#

yup

shadow thorn
#

but at x = 0 its -2

fathom ridge
#

the actual value of he function doesnt matter

charred pelican
#

your question should be "why does this limit exist"

fathom ridge
#

you just need to see what it approaches

shadow thorn
#

Ohhh

#

so limit is different from equalling?

#

basically

#

is equalling a word

#

i meant equality

charred pelican
charred pelican
#

Basically if there is a point which exists when the limit approaches some "x" then the limit exists

#

given that the LHL and RHL are the same

shadow thorn
#

soo

charred pelican
#

it is different

shadow thorn
#

the limit is not always the same as the value of the function at that point

shadow thorn
#

got it

#

thx

#

.close

marsh citrusBOT
#
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zealous glacier
marsh citrusBOT
zealous glacier
#

how to do part f

oblique grove
#

in the numerator

cloud field
oblique grove
#

24^(x+1)

#

can be written as (2^3 * 3)^(x+1)

zealous glacier
#

oh

oblique grove
#

the 8^-1

#

goes to the denominator

#

as a^-b = 1/a^b

#

so the Dr is (6^2x*8)

#

the 6 is written ad 2*3

#

and the 8 as 2^3

#

so the Denominator is (2*3)^2x X2^3

#

using the laws of exponents it can be finally written as

#

2^x*3^(1-x)

zealous glacier
#

cheers mate

#

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dire pulsar
#

I need help doing calculus

marsh citrusBOT
dire pulsar
#

Could someone provide me basic calculus worksheets that will help me understand because I am learning.

marsh citrusBOT
#

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twilit musk
#

In an alien world, there’s a peculiar plant known as the Starlight Creeper. This plant has a unique growth pattern; from each of its stems, three new stems emerge every year. This process starts with a single stem and continues for 10 years. Determine the total number of stems that the Starlight Creeper will have at the end of the 10th year, including the original stem.

twilit musk
#

So I understand that in the beginning theres one stem, then 1+3, then 1+3+(12), so basically its f(n) = f(n-1) + f(n-1)*3 right where f(0) = 1

#

is that correct?

#

in any case, how do I proceed?

#

i asked chat gpt and it formed a geometric series which I kind of understand where it comes from but Im hoping for a detailed explanation for an understanding so that I can solve similar questions

charred pelican
#

We have 1 stem

#

in 1 year we have +3 stems

#

so we have 4 stems

twilit musk
#

yes

charred pelican
#

In the next year, we get 3 stems from each stem

#

so we get 12

#

so we have 16

#

in the third year,
we have 3 stems growing from one and we have 16 stems
so we get 48 stems

#

Can you see a pattern?

twilit musk
charred pelican
twilit musk
#

so the sequence is 1 + 3 + 12 + 48 and so on

charred pelican
twilit musk
#

take the previous addition multiply by 3

#

?

charred pelican
#

at the origin of year, we have 1 stem

#

at the end of one year, we have 4

#

at the end of second year, we have 16

#

at the end of third year we, have 48

charred pelican
twilit musk
charred pelican
brittle dust
#

there’s an easier way to do this

#

what the sequence is is an arithmetic sequence

#

this is the formula for it

twilit musk
brittle dust
#

a sub n = the number term you are trying to find

charred pelican
brittle dust
#

a sub 1 = the first term

brittle dust
left wadi
#

isnt it geometric series?

twilit musk
#

if anything it should probably be a geometric series

#

right

brittle dust
#

geometric is when there is a common ratio

twilit musk
#

I wanted to understand why

left wadi
#

a_10 gives you 28

charred pelican
left wadi
#

whats way too low

charred pelican
#

uhm

twilit musk
charred pelican
#

am i being dumb

brittle dust
#

the difference between each term is 3

#

when we add by increments of the same number in a sequence it’s called arithmetic

#

geometric is when we multiply each term by the same quantity

#

which is not the case here

charred pelican
#

For, T0 =1

for T1 = 4

for T2 = 16

twilit musk
charred pelican
brittle dust
#

oh EACH stem grows 3

#

ok then this is geometric

#

my bad

charred pelican
#

which will be your answer

brittle dust
#

you can use this for geometric

cunning jackal
#

Because T1 is at the start of the first year

twilit musk
charred pelican
brittle dust
#

a sub 1 = 1 (because we start with 1 stem)

and we let n = 11

charred pelican
#

Both of them mean the same stuff

left wadi
#

if a_1=1 then a_2=3* a_1 then a_3=3* (a_1+a_2) and so on then a_n=3*(a_1+a_2+...+a_(n-1))

brittle dust
#

so it’s just 3^10

twilit musk
brittle dust
#

59,049 stems

left wadi
#

wouldnt it?

brittle dust
#

oh true

left wadi
#

and T_2=9 but its T_2=16

brittle dust
#

ok im out of my league here lol

twilit musk
#

common ratio is 4 right

left wadi
#

16-9=7

cunning jackal
left wadi
#

and 16/9 =/= 4

twilit musk
cunning jackal
#

Idk why this is being complicated here when you had the answer in your first message

cunning jackal
#

You said it yourself f(n) = f(n-1)+3f(n-1)

#

=4f(n-1)

twilit musk
cunning jackal
#

Depends on what you call T1.

twilit musk
cunning jackal
#

1,4,16,64..

#

That is our series

twilit musk
#

yes this

left wadi
#

ok

twilit musk
#

well ty guys

left wadi
#

i just leave it out to you

twilit musk
#

.close

marsh citrusBOT
#
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marsh citrusBOT
#
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hoary veldt
#

Hi, can anyone help me with the integral of $\sqrt{tanx}$

elfin berryBOT
#

Aetherfly

novel juniper
#

$\int \sqrt{tan(x)}dx$?

elfin berryBOT
#

Why am. I here

hoary veldt
#

yes

#

ive heard that its very hard

novel juniper
#

ok, so which method do you think you should use

hoary veldt
#

substitution at fist

novel juniper
#

cool

#

what sub

hoary veldt
#

or no

#

sqrt cosx

novel juniper
#

hint tan(x)=u works well

hoary veldt
#

would be better

hoary veldt
#

I never thought ofthat

novel juniper
#

you first multiply and divide by $sec^2(x)$

elfin berryBOT
#

Why am. I here

hoary veldt
#

like how do I know

novel juniper
#

try it

hoary veldt
#

but

#

how do i know

#

to do it

novel juniper
#

as in how to think of it?

hoary veldt
#

(dont say intuition)

hoary veldt
novel juniper
#

I won't

#

I basically want to introduce the derivative into the integrand somehow

#

to perform a u-sub

#

as I know that $d(tan(x))=sec^2(x)$

elfin berryBOT
#

Why am. I here

hoary veldt
#

hmm

novel juniper
#

so you get $\frac{\sqrt{u}}{1+u^{2\ }}$

elfin berryBOT
#

Why am. I here

novel juniper
#

right?

#

wait, this may not work

#

let me try

hoary veldt
#

oh

novel juniper
#

one min

#

ok, I was sort of wrong

#

$tan(x)=u^2$ works better

elfin berryBOT
#

Why am. I here

novel juniper
#

allowes you to elimiate the root too

hoary veldt
#

hmm

novel juniper
#

makes sense?

hoary veldt
#

wait let me try

#

to di it

#

do*

marsh citrusBOT
#

@hoary veldt Has your question been resolved?

marsh citrusBOT
#
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dreamy hull
#

Hello, does anyone know why this change is legal?

dreamy hull
#

Does it have something to do with complementary angles? I know that sin(x) = cos(y) if and only if x+y=pi/2.

novel juniper
#

yes

dreamy hull
#

but how would it apply in this case?

#

the other thing I know is that cos and sin are equal at 45°

#

but I don't quite understand what was done there

novel juniper
#

$sin(\alpha+pi/4)=cos(pi/2-(/alpha+pi/4))$

elfin berryBOT
#

Why am. I here

marsh citrusBOT
#

@dreamy hull Has your question been resolved?

dreamy hull
#

but how do I get to the cos(a - pi/4) expression?

#

ah, by the parity of cosine cos(x) = cos(-x)

#

thanks

#

.close

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inner grove
#

Can someone explain me please, what does "df" over equal sign means in this notation?

inner grove
#

In my book about probability it's called upper bound of sequence of events A_n

#

I think it's some kind of convergence, but what exactly

#

I see on the internet, there is word "def", rather than "df". I think if that's the same, cause I don't see anyone to use df

#

but it might be it

#

I will wait for more answers, cause I am not quite sure

static trench
#

yeah that is why I deleted since I wasnt 100% sure and dont want to mislead you

inner grove
#

k, thank you

#

.close

marsh citrusBOT
#
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neon imp
#

How do I confirm this operation is closed?

marsh citrusBOT
neon imp
#

I also have the addition, if needed

#

Can I do neutral element of addition * vector = neutral element of addition?

marsh citrusBOT
#

@neon imp Has your question been resolved?

neon imp
#

<@&286206848099549185>

marsh citrusBOT
#

@neon imp Has your question been resolved?

neon imp
#

<@&286206848099549185>

remote granite
neon imp
#

Damn, I really need to understand this.

#

Cuz if a scalar times the vector comes to something, it also has to be inside the same subspace so it is closed under scalar multiplication.

marsh citrusBOT
#

@neon imp Has your question been resolved?

neon imp
#

.close

marsh citrusBOT
#
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craggy skiff
#

help

#

If I were to add 50% to a number, how could I reverse this? like if I was given a number and was told it had 50 percent added to it, how could I get its original value?

sleek lake
#

times 2 divide by 3

craggy skiff
#

ty

marsh citrusBOT
#
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past shard
#

Does anyone mind explaining why $\frac{d}{dx}\left(\frac{\sqrt{1^2+\left(15-x\right)^2}}{2.5}\right) = \frac{0.4\left(x-15\right)}{\sqrt{x^2-30x+226}}$ and not $\frac{1}{6}+\frac{\frac{2}{5}x-6}{\sqrt{1^2+\left(15-x\right)^2}}$?

elfin berryBOT
#

Punisher

honest berry
#

hey guys

#

can someone help me

tiny patrol
#

try simplifying the fraction, to 1/2.5(sqrt(16-x^2)) and apply differentiation rules

#

@honest berry go to a closed help channel and open it

tiny patrol
#

@past shard hint:

#

this will make things much easier

tiny patrol
tiny patrol
#

now can you find the derivative of that?

past shard
tiny patrol
#

you have 1^2 + (15-x^2) correct?

past shard
#

No. I have sqrt of 1^2 + (15 - x)^2

#

Oh

tiny patrol
#

that changes things then

past shard
#

That's my bad; I didn't indicate that it was the quantity (15 - x)^2

tiny patrol
#

and letting the inside be

#

sqrt(1 + (15-x)^2)

#

step by step, using the chain rule

#

and tell me where you will get

past shard
#

d/dx [√1^2 + (15 - x)^2] => 1/2 • d/dx [1/√1^2 + (15 - x)^2]

#

Am I right so far?

tiny patrol
#

you are missing something, apply the chain rule correctly

#

you need to multiply the whole fraction by the derivative of the inside of the square root

#

so (1/2 • d/dx [1/√1^2 + (15 - x)^2]) * d/dx[1 + (15-x)^2]

#

if you have done it correctly it should be this

#

dont forget to multiply this whole thing by the constant at the start though!!

#

1/2.5

past shard
#

Right. Ok, so that would equal (-1)(15 - x)(1/√1 + (15 - x)^2)

tiny patrol
#

not quite, how did you get the -1 at the start?

past shard
#

from d/x[(15 - x)^2]

#

well, from the interior function

tiny patrol
#

ohhh yes, i forgot to write it down on the final answer!

#

the minus is there in the last step

past shard
#

Right. So, the final answer should then be (x – 15)/6.25(√1 + (15 - x)^2. Right?

tiny patrol
#

why 6.25?

#

the constant is 2.5

past shard
#

2.5^2 = 6.25

#

The denominator must be squared, no?

tiny patrol
#

nono you have placed the constant outside the derivative so you just multiply it at the end

#

d/dx[c * f(x)]= c * d/dx[f(x)]

#

are you there? do you need me to explain any further on that?

past shard
#

Sorry. I just re-derived the original function (d/dx[(√1^2 + (15 - x)^2)/2.5]), and I got a very similar answer to my original answer (minus the 1/6).

#

^ I thought the quotient rule of derivatives stated that the derivative of a fraction is the derivative of the numerator multiplied by the denominator minus the derivative of the denominator multiplied by the numerator, and all divided by the denominator squared.

#

Wait. I was right this whole time 😆; the answer I looked up was just in decimal form (namely, 0.4(15 - x)/√x^2 -30x +226)

#

0.4 => 2/5 lmbo

#

Anyways

#

Thanks @tiny patrol

#

.close

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#
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flat bear
#

This is the first exercise in chapter 4 of the book think bayes 2 and i can't understand why they choose the prior for getting a hit as uniform between 0.1 and 0.4? I don't see any motivation for that in the question, imo either you use the info given to make a more accurate prior or you just do a uniform between 0 and 1. Anyone understand this choice? Hopefully this is ok as a statistics question, feel free to remove if its not appropriate to ask that here

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#

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tawny herald
#

How do I find the center on the ellipse based off the plotted points without looking at the graph?

sand fable
#

average those 2 points to find center

tawny herald
#

.close

marsh citrusBOT
#
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balmy vault
#

Im trying to find the real and imaginary values of the function g(z) = sin(1/z)

balmy vault
#

Im kinda stuck at (e^(i/z)-e^(-i/z))/2i

still temple
#

euler’s formula for the trig functions?

balmy vault
#

imma try 2 sec

stray hound
balmy vault
#

wait how would i then spilt the z=a+bi inside the cos and sin

still temple
#

you dont

stray hound
#

1/(a+bi) = (?) + (?)i

balmy vault
#

then every part would be imaginary no?

still temple
#

because e^(a + bi) = e^a(e^(bi))

balmy vault
still temple
#

1/(a+bi) = (a - bi)/((a+bi)(a-bi))

#

simplify that

#

again the last time i was messing around with trig in C i used the taylor series

balmy vault
#

(a-bi)/(a^2-b^2)

#

?

still temple
#

equal to a/(a^2-b^2) - bi/(a^2-b^2)

balmy vault
#

yeahh oooh i think i got now ty

still temple
#

now expand into cos x + i sin x in your formula thing

#

also can you tell me once you have your answer i might need it for a coding project lol

balmy vault
#

Sure give me little time tho something came up i gotta go for 5 ish min

marsh citrusBOT
#

@balmy vault Has your question been resolved?

balmy vault
#

wha

#

well i found a section in my book after i was stuck

#

sin(z)=sin(x)cosh(y)+icos(x)sinh(y)

#

i am assuming i can use this property here no?

still temple
#

where z = x + iy? yes definitely

#

just gonna screenshot this rq for whenever i need brute force complexexp rq

balmy vault
#

This is correct no? Sorry bout handwriting and Angle

still temple
#

how do x and y relate to z

balmy vault
still temple
#

oh ok

balmy vault
#

Isnt the real part denoted by x and the imaginary by y?

still temple
#

yes

#

so it would be sin(x + iy) = sin(x)cosh(y) + i cos(x)sinh(y)

balmy vault
#

Ye

#

But I got sin(1/z)

still temple
#

now substituting that into your formula seems to match that paper

balmy vault
#

^^ yay

still temple
balmy vault
#

Ty for help ^^ ❤️.close

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cobalt garnet
#

Suppose that two cards are selected at random from a standard 52-card deck. What is the probability that both cards are less than 10?

Since there are 4 suits and each of them has 8 cards that are less than 10 we get 32 cards that are less than 10 in a 52-card deck. To get the probability we divide 32C2 by 52C2?

slim spire
#

👍 that's correct, there's a way that has a more simplified answer if you do (chance of first <10 card)*(chance of second <10 card given the smaller deck)

cobalt garnet
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Thanks

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odd sparrow
marsh citrusBOT
odd sparrow
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Is my working out correct?

vernal pike
#

Yes

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balmy vault
#

im trying to sketch f(z)= zi where Re(z) > 0

marsh citrusBOT
balmy vault
#

so let z = x+yi so f(z) = xi-y

#

x would still be the real part of the equation so would this be the functional equivalent of x*1

#

?

#

which would mean that this would essentially be the same sketching z with Re(z)>0

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feel free to ask questions if i didnt properly explain myself

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sharp mauve
#

0,3 <= π^2/8-0.5arctan(N) how can i find n without trail and error?

sharp mauve
#

This was my attempt

zenith dragon
#

i'd proly do it by trial and error

sharp mauve
#

why?

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tidal wasp
#

help

marsh citrusBOT
tidal wasp
#

hello

#

i need help

#

on this question

winter nest
#

you have only considered one possibility, the magnets could be UDU or UUD

tidal wasp
#

yes

#

added them up and i get 9/16

#

i tried tht but it doesnt work sadly

winter nest
#

is there a chance that the quesetion is written wrong and wants you to do at least 2 pointing upwards?

tidal wasp
#

idk

#

its unlikely

#

but i could try the answer for what u said

#

if so i would have to include UUU

winter nest
#

yeah

tidal wasp
#

yh it isn't 10/16 either

winter nest
#

yeah you have done the probabilities wrong

tidal wasp
#

oh

winter nest
#

the answer i got was 3/4, but working out P(UD)xP(DU) + P(UU)xP(UD)

tidal wasp
#

yes thats correct

#

could u draw a ven diagram

winter nest
#

so the probabilities you are wanting is 3/4 x 3/4 + 1/4 x 3/4

tidal wasp
#

yeah

#

what about these two questios

winter nest
#

you want to work out P(UDD) as that is the only configuration that will have only one magnet pointing upwards

tidal wasp
#

so would that be 3/4 *1/4

winter nest
#

yeah thats correct

tidal wasp
#

P(DDD)

#

would it be 3/16

winter nest
#

you will have to read the question carefully for that one

tidal wasp
#

tbh

#

i need to work on how i read that question

#

but would part D u just need to find P(DDD)

winter nest
#

yeah you need to find P(DDD) but when you read the question you can see that the left most magnet is always U, so the probability is 0

tidal wasp
#

oh

#

so 0 * 1/4

winter nest
#

yyeah exactly

tidal wasp
#

oh

#

can i also get help on a kinematics question

winter nest
#

i can try, i havent really done any kinematics for about 3 or 4 years but i can have a look and point you in the right direction if i dont understand it

tidal wasp
#

alright

#

what about a vectors questin

winter nest
#

yeah i can help with that

tidal wasp
winter nest
#

with this one, if you have the speed of the yacht u = v then they are both heading in the same direction, so the least value of u would have to be going in the opposite direction to v

tidal wasp
#

alright

#

so u = -v

winter nest
#

thats what i think yeah

tidal wasp
#

nope its wrong

#

i think it needs to include a and b

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ah don't worry anyway

#

thank u for your help

#

may your pillows be forever cold to have a good sleep

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wintry moth
#

Help

marsh citrusBOT
wintry moth
#

(╯°□°)╯︵ ┻━┻

#

.flip

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celest geyser
#

quadratic formula

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urban grove
#

How much weight of lead do I need for a 52 cm sphere made out of concrete, if I want the desired weight to be 220 kg?

The sphere diameter cannot change, only the lead and concrete volume.
Calculated with 2200 kg/m3 concrete volume and 11 340kg/m3 with lead volume.

52 cm sphere = +- 162 kg, that would simply mean I need 58 kg lead core of a 21,4 cm diameter.
However, while inserting the core, there needs to be taken in consideration, that also the same volume of concrete needs to be removed. Which is around 11,3 kg with that diameter and concrete volume. And THAT again... would mean I need to add another 11,3 kg of lead to the core ?
Which would mean -> 22,7 cm diameter of the lead core, which again removes roughly 13,5 kg of concrete and again calculation of core... I dont think I am going the right way... I would like to reach the exact weight of lead needed, which doesnt get me there by this approach.

(I am long gone from math classes, sorry, be nice to me.)

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@urban grove Has your question been resolved?

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@urban grove Has your question been resolved?

urban grove
#

<@&286206848099549185>

marsh citrusBOT
#

@urban grove Has your question been resolved?

molten moss
#

Then, the only unknown is the radius/diameter of the lead sphere inside. Let me try and walk you through the theory

#

Let's fix some notation: $m$ is your desired total mass (220kg), $\rho_c$ is the density of concrete (2200 kg/m3), $\rho_{l}$ is the density of lead (11340kg/m3), $R$ is the outer radius (52/2 cm = 26 cm) and $r$ is the radius of the inner sphere.

The weight of the inner lead sphere is then the volume of it, times the density: $\frac{4}{3} \pi r^3 \rho_l$, the weight of the concrete hull around it is $\frac{4}{3} \pi (R^3 - r^3) \rho_c$, so we have that the total mass is $m = \frac{4}{3} \pi r^3 \rho_l + \frac{4}{3} \pi (R^3 - r^3) \rho_c$. Since the only unknown is $r$, we should be able to solve this equation for $r$, let's do that

elfin berryBOT
#

Lartomato

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molten moss
#

Just reshuffling terms gets us $\frac{m - \frac{4}{3} \pi R^3 \rho_c}{\frac{4}{3} \pi (\rho_l - \rho_c)} = r^3$

elfin berryBOT
#

Lartomato

molten moss
#

goddamnit i'm not asking a question i'm responding to one

#

Simplifying that and taking the third root, we get

$\sqrt[3]{ \frac{3m}{4 \pi (\rho_l - \rho_c)} - \frac{R^3 \rho_c}{\rho_l - \rho_c}} = r$

elfin berryBOT
#

Lartomato

molten moss
#

If you trust this, then the radius of your inner lead sphere should be 11.487cm

molten moss
#

and the double-check does pretty well

#

@urban grove let me know if that helped you! good luck with your extremely heavy spheres

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urban shard
#

Looking at a quick proof for symmetry in A^T A

urban shard
#
It is the dot product of row i of AT (column i of A) with column j of A. The (j, i) entry
is the same dot product, column j with column i.```
#

😭 Lol why is this the case? I don't see it

#

,, (row i){A^T} \cdot (col j)A = (row i){A} \cdot (col_j){A^T}

elfin berryBOT
#

nyxie9151

urban shard
#

they're equal?

iron meadow
#

1st column = 1st row of transpse

marsh citrusBOT
#

@urban shard Has your question been resolved?

urban shard
#

i mean like

#

i'm talking about symmetry in A^T A

#

What does this mean? Maybe i'm a bit dense now but yeah

#

Could you explain that bit

urban shard
#

actually i got it

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half portal
#

hello, i'd appreciate some help with this problem, i know there's probably a formula but i would like to know if i could integrate shape (i) 👍

half portal
#
  • if i put it in a cartesian plane, maybe try to get a function for the horizontal crossection, i assume it would be y=(1/2rx+r), because of the gradient and the fact that the integration would start from y=r, is this the correct approach? can't seem to get it right
stray hound
#

it's the right idea, but I think your line is wrong since it should depend on h in some way

#

connect the points (0,r) and (h,3r/2)

#

then find the volume

half portal
#

then the line should be y=(rx/2h)+r?

#

got it, it was (19pi/12)(r^2)(h) thanks

#

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shut stone
#

find the real number m so that the equation has at least two real solutions

shut stone
#

!status

marsh citrusBOT
#
What step are you on?
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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
shut stone
#

1

#

<@&286206848099549185>

spark siren
#

just try some values. assume x = 0. does the equation hold?

shut stone
#

it does not hold

spark siren
#

sorry, not x = 0. m = 0.

shut stone
#

it does

spark siren
#

for m = 0 you get 2 soluions for x?

shut stone
#

yes

#

wait no

#

yes

#

x=+-sqrt(e)

spark siren
#

now look at your solutions a) to f) which contains 0?

shut stone
#

did you mean a and c?

spark siren
#

a and c does not contain 0, so they cant be right.

shut stone
#

yes

#

I also took the derivative and I got 2x(1/x^2-m)=0, and for m=-e^(-2) we have 1/x^2=-e^(2) which is false. So we also eliminate d

#

and e and f

#

so it must be b

#

right?

spark siren
#

why not f?

shut stone
#

we have 1/x^2=m in the derivative so m cant be negative

#

and it need to have at least two points in which is 0

#

except for x=0

spark siren
#

why do you use the derivative?

shut stone
#

I thought it would be easier

spark siren
#

easier for what?

shut stone
#

if it changes sign at a point then it has at least one solution in that interval

spark siren
#

m=-1 has to solutions:

shut stone
#

oh well

#

what would be the better approach

spark siren
#

just try some appropriate values.

shut stone
#

ok ill try

#

so there is m=e^(-2)

#

so we check now only d and e

#

and since we also have m=-1 the answer is f

#

thank you for help

#

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urban cradle
#

quick question, does e stand for joules or p stand for joules

frozen delta
#

J stands for joules

#

but

urban cradle
#

J?

#

yeah ik

frozen delta
#

Joules are a measure of energy

#

so

urban cradle
#

but like u have E P T

#

aahh

#

so E

frozen delta
#

E

#

yeah

#

:)

urban cradle
#

thx

#

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rare pollen
#

You want to buy a new sports car from Muscle Motors for $44,300. The contract is in the form of a 72-month annuity due at an APR of 6.05 percent. What will your monthly payment be?

rare pollen
#

hi

storm fern
#

you could use this calculation to find the total price

rare pollen
#

uh

#

i have not seen that equation before

storm fern
#

n is expressed for the n-th value of a certain period which is annually increased based on the question

#

so you have 72 months right?

rare pollen
#

correct

storm fern
#

how many years would it be

rare pollen
#

6

storm fern
# storm fern

the n would be the exponent you use on this equation

#

and the i would be the annual percentage rate

#

which is the interest

rare pollen
#

right

storm fern
#

and Mo is the price offered by Muscle Motors

#

which is 44.300

rare pollen
#

right

storm fern
# storm fern

so what's the total price would be by using this formula?

rare pollen
#

well i have to first fit everything into the equation

storm fern
#

after you found the total price, divide it by 72 as you have to find the amount to pay monthly

rare pollen
#

72 = 44,300 (1 + 6.05) 6 ?

#

that might be wrong

storm fern
#

72 is not the total price of it

rare pollen
#

o the left is what we are finding out

storm fern
#

right

rare pollen
#

44,300 (1 + 6.05) 72. ?

storm fern
#

$44.300(1+6.05)^6$

elfin berryBOT
rare pollen
#

ah i see

#

5,439.242.58