#help-0

1 messages · Page 467 of 1

buoyant saddle
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my fault gang

proven leaf
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so we must look at both the positive and negative cases :)

azure axle
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oh

proven leaf
azure axle
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i didn’t understand we were actually plugging it into y

buoyant saddle
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another way to think of it

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y^2 - 1 = 0

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then factor

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difference of two squares

azure axle
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well thank you . just got back in math

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.close

lone heartBOT
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fast nest
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hi i was wondering if i could get help w these 2 tables. i thought i knew what i was doing but what i ended up with wasn’t right so if i could just get some help that’d be great

proven leaf
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the definition of a linear function is that the slope remains the same

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for the first table

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can you find $\frac{Q_2-Q_1}{t_2-t_1}$?

ocean sealBOT
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PajamaMamaLlama

fast nest
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90.02-95.01/2-1?

lone heartBOT
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@fast nest Has your question been resolved?

proven leaf
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,calc (90.02-95.01)

ocean sealBOT
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Result:

-4.99
proven leaf
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so that is -4.99

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now find $\frac{Q_3-Q_2}{t_3-t_2}$

ocean sealBOT
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PajamaMamaLlama

fast nest
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oh yeah it’s -4.99 as well

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sorry i’m not getting notifs

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fast nest
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.reopen

lone heartBOT
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proven leaf
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lol no worries

fast nest
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i believe this one is linear but i don’t know how to set up the problem to convert it to the equation

lone heartBOT
#

@fast nest Has your question been resolved?

lone heartBOT
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ember pelican
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im just confused on how to find the r(x) i know that 1/x^5 is the h(x)

lone heartBOT
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@ember pelican Has your question been resolved?

ember pelican
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<@&286206848099549185>

arctic river
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what is formula for the individual slices of the cylinder

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@ember pelican

ember pelican
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This is using the shell method tho right?

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Not the disk method

arctic river
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formula for cylndrical shells is what

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w.r.t x

ember pelican
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Can't figure how what r(x) would be

arctic river
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ok what is r(x) and h(x) in this case

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u draw a diagram

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what variable is responsible as the slice gets closer and closer to b

arctic river
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this isnt really representitive of the area that u need to find

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its underneath 1/x^5

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above y=0

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between x values

ember pelican
arctic river
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ok r(x) is x

ember pelican
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honestly i probably shoulda tried that first since thats what it was for two other problems

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thx

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.close

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#
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raw jetty
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find the ammount of odd coefficients of the expansion of (x+y)^1000

raw jetty
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this is scary honeslty

woeful pulsar
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Do you know how to find the coefficients?

raw jetty
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depends on weather i know the method your talking about or not

woeful pulsar
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Do you have any useful formulas for the coefficients?

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Formulas that maybe make it easier to check whether it is odd or even?

raw jetty
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uh maybe the choose function one?

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honestly no

woeful pulsar
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how about one involving factorials

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checking whether a product is even might be much easier

raw jetty
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dont know any

sour mica
raw jetty
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ok

woeful pulsar
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do you know how the choose function can be written with factorials?

raw jetty
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uh its like n!/k!(n-k)!

woeful pulsar
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yeah, so you do know how to write it with factorials, so the problem basically becomes determining whether this is even or odd

raw jetty
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iirc n is the row and k is the thing from left to right or something

woeful pulsar
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I'll introduce this idea of a valuation, $\nu_2:\mathbb{Q}\to\mathbb{Z}$, it basically counts ``how many times 2 divides this rational number''

ocean sealBOT
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Element118

woeful pulsar
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The relevant relations are $\nu_2\left(\frac{a}{b}\right)=0$ if both $a,b$ are odd, and $\nu_2(2k)=\nu_2(k)+1$.

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(Exercise: Show that this is a well-defined function.)

ocean sealBOT
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Element118

raw jetty
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nmv im dumb lmao

mortal trellis
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if you had natural numbers, how often is 2 in the prime factorization

woeful pulsar
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how many times (2 divides) this rational number

woeful pulsar
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should have gone for an easier approach tbh, this valuation thing might be overkill

raw jetty
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uh what can i do with it?

lone heartBOT
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@raw jetty Has your question been resolved?

woeful pulsar
ocean sealBOT
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Element118

woeful pulsar
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The alternative is to look at the power of 2 in the prime factorisation, and that approach is equivalent

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so do whatever's more comfortable

raw jetty
woeful pulsar
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since the approach is easier

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and equivalent anyway when you unpack it

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you want to find the number of powers of 2 in the prime factorisation of $\frac{n!}{k!(n-k)!}$

ocean sealBOT
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Element118

mortal trellis
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I mean its not that easy with binomial coefficients. the answer is given by lucas theorem but I am not sure how that can be motivated well

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and the proof does something completely different

raw jetty
woeful pulsar
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so the subproblem is to find the number of powers of 2 in a factorial

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if we can solve that for a factorial, we just need to combine the result for the numerator and the denominator to get the entire thing

raw jetty
woeful pulsar
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but it's not very easy to work with now

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perhaps if we can write it as $n-$something we can make it easier

ocean sealBOT
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Element118

cursive badger
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But I don't think he'll know about that...

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It's not so common to use.

raw jetty
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find the "something" i mean

woeful pulsar
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n=n/2+n/4+...+...

something=n-(floor(n/2)+floor(n/4)+...)
=(n/2-floor(n/2)+n/4-floor(n/4)+n/8-floor(n/8)+...)
={n/2}+{n/4}+...

might still be unwieldy, my next thought would be perhaps looking at the numbers in binary, there's a good chance that would help

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since we have a lot of floor(n/2) and that's naturally shifting the integer in binary

mortal trellis
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pretty sure base 2 will help

woeful pulsar
cursive badger
mortal trellis
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the correct answer is expressed using the digits of base 2

woeful pulsar
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we can always look at small cases to try checking for a pattern

cursive badger
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It's like not so common...

raw jetty
mortal trellis
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write n in base 2

woeful pulsar
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writing n in base 2, and k in base 2, then you may be able to see when n! has the same number of powers of 2 as k!(n-k)!

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maybe look at doing k + (n-k) = n and think what happens if there are no base-2 carries in the addition

raw jetty
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wtff

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yea i actually dont understand a thing of what your talking about sorry 😭

woeful pulsar
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Show that when you write $n=\sum_{i=0}^ka_i2^i$ in base 2 where $a_i\in{0,1}$, we have
[\sum_{i=1}^\infty\left\lfloor\frac{n}{2^i}\right\rfloor=\sum_{i=0}^ka_i(2^i-1)]

ocean sealBOT
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Element118

woeful pulsar
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(think about how the left and right hand side look like in binary)

raw jetty
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sorry had s9mething to do

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the rhs would like flip all yhe previous digits

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the lhs would be uh

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would it not be the binary representation of n?

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wait no

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ok wth im not seeing it

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let n=15
7+3+1
111+11+1
1011

a_i from i 1 to 4 would be
1110
checking
1+3+7+0

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huh how do i generalize it :(

lone heartBOT
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@raw jetty Has your question been resolved?

#
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heavy prairie
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z^2 = 6i

lone heartBOT
heavy prairie
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I want all the z's

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I assume there will be two since they are the roots

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I forgot how to continue

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sqrt both sides might be a good start

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but after that it is a blur

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z = sqrt(6i)

uneven isle
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rewrite 6i as [(sqrt6)(cis(pi/2 + 2k pi))]^2

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cis = cos + isin

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its informal notation but used widely enough so i will just keep referring to it as cis

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then naturally square root both sides to find the roots

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then apply de movire's theorem and it should be complete

heavy prairie
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alright I will try to do that

uneven isle
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k is just some integer

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for convenience we will let it take on 0 and 1

heavy prairie
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Is that the same thing?

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The cis thing confused me ngl

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I also called k n instead

uneven isle
heavy prairie
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oh yeah

uneven isle
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make sure u define n tho as an integer

heavy prairie
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i see that now

uneven isle
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just out of habit

heavy prairie
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ok so hold on

uneven isle
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for more formal exams or writings it should be expected for you to define n, the +2pi n is there for periodicity

heavy prairie
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ye i get i get it

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let me correct it

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or attempt to

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If that is correct I can determine the value of cos and sin

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because I know the angle

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but how did you determine the angle was 90 degrees?

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or pi/2?

uneven isle
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out of practice ig?

heavy prairie
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Is it just because we say the complex axis is perpendicular to the real axis?

uneven isle
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u can just evaluate it to show that it is i

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or u can say complex axis is perpendicular like u suggested

heavy prairie
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so is the angle always pi/2?

uneven isle
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for i?

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yes

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for other values? no

heavy prairie
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im not sure i understand

uneven isle
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so for normal roots of unity

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liket say z^n=1

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ur angle for ur RHS expression would be just 0+2npi

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the angle depends on what u are trying to find roots for

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In mathematics, a root of unity, occasionally called a de Moivre number, is any complex number that yields 1 when raised to some positive integer power n. Roots of unity are used in many branches of mathematics, and are especially important in number theory, the theory of group characters, and the discrete Fourier transform.
Roots of unity can b...

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this might help if u want to have a read through

heavy prairie
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I am not getting the right answer

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if x is a member of Z

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sry

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I mean if n or k is a member of Z

uneven isle
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dont have to apologise

heavy prairie
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then cos(pi/2 + 2pi n) should be 0?

uneven isle
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yes that is right

heavy prairie
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and sin(pi/2 + 2pi n) would be 1

uneven isle
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yep

heavy prairie
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yeah then i have 0 + i

heavy prairie
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wait

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i^2

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so -1

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but uhh

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that is not the right answer

uneven isle
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oh i monkey brained

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the trig expression isnt meant to be squared

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just only the sqrt(6) is meant to be squared

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should be
z^2 = (sqrt6)^2 * cis(pi/2 + 2kpi)

heavy prairie
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okay

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i will try to write that down

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isn't (sqrt6)^2 just 6?

uneven isle
heavy prairie
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ok

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is 6 just c or something

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in the formula?

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what is the formula?

uneven isle
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there isn't really a formula , at least i was never taught one

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i mean, u could generalise it to taking nth root as

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z^n = r(e^(ix)), where x is some real such that r(e^(ix)) will represent ur RHS expression

heavy prairie
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i am running into the same problem

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where this isn't the answer

uneven isle
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show ur working out

heavy prairie
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first term equals 0

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second is i

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then when i square z

uneven isle
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yes and ur lhs is still z^2

heavy prairie
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i get sqrt(i)

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that's not the answer

uneven isle
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u need to apply De moivres theorem or use euler's form

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and sqrt6* sqrt(i)is a root

heavy prairie
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Okay I am still confused

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z^2 = 6i

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z^2 = 0 + 6i

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where a = 0

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and b = 6

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then I get the modulus of z

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which is the same as r?

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I think

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again I am confused so I don't know

uneven isle
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z^2=6i = (sqrt6)^2 * (cis(pi/2 + 2kpi))
=>
z= sqrt6 * [cis(pi/2+2kpi)]^1/2
=>
z=sqrt6[ (cis(pi/4 + kpi)]

heavy prairie
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That doesn't clear it up for me

uneven isle
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dont use x+iy form

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it isn't helpful here

heavy prairie
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I am turning it from rectangular to polar

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You can do it in your head

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I can't

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|z| = r = sqrt(0 + 6)

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so now that explains to me how you arrived at sqrt6

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Assuming that is right

uneven isle
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mhm ok lets just start over, i will try my best to show not skip any steps

z^2 = 6i = 6 [ cis(pi/2 + 2kpi) ]

heavy prairie
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De Moivres says z^n = r^n (cos(n theta) + isin(n theta))

uneven isle
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if z = r cis theta yes

heavy prairie
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bro this cis stuff

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is just confusing to me

uneven isle
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ok i will stop using it

heavy prairie
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I understand it is just the shorthand

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for (cos(n theta) + isin(n theta))

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well I say I understand

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but I don't know

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I assume that is what cis means

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but I don't know

uneven isle
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cis theta is just cos(theta) + i sin(theta)

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regardless, i wont use the shorthand

heavy prairie
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going from here

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|z| = r = sqrt(0 + 6)

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is that true?

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is |z| = r

uneven isle
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yes that is true

heavy prairie
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ok

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so I put my sqrt6 into De Moivres

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all my givens that I can figure out

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z^2 = (sqrt6)^2 (cos(2 theta) + isin(2 theta))

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then you said the angle was pi/2

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I have no clue how you got there

uneven isle
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i would avoid working out in your current order but i will xplain why in a few steps

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for now, just to clarify

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what demovire's is saying is just (cosx+ i(sinx))^n = cos(nx) + isin(nx)

heavy prairie
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Can you summarise the order

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in words

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Your recommended order

uneven isle
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let me wirte down on paper and i will just send an image, easier htis way

heavy prairie
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Given a complex number in rectangular form

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no wait in this case it isnt a complex number, it is a squared complex number

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this is so confusing to me

uneven isle
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@heavy prairie my handwriting isn't the neatest in the world so lmk if anything is too difficult to read

heavy prairie
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i will read this in a sec

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Arg(0 + 6i) is the angle right?

lone heartBOT
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@heavy prairie Has your question been resolved?

lone heartBOT
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@heavy prairie Has your question been resolved?

heavy prairie
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<@&286206848099549185>

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z^2 = 6i

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goal is to find roots

alpine sable
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ok

heavy prairie
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I rewrite it as z^2 = 6i + 0

alpine sable
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i know

heavy prairie
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Brother

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Actually

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Nah nvm

alpine sable
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use z = a+bi

heavy prairie
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yes Daniel yes

heavy prairie
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<@&286206848099549185>

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$z^2 = 6i = 0 + 6i = a + bi$\\De Moivre's Theorem tells me that $z^n = r^n(cos({\theta}n) + isin({\theta}n)$\\I don't know Theta or r, but to find r I can:\$z^2 = 0 + 6i\Longrightarrow z = \sqrt{0 + 6i} \Longrightarrow |z| = r = |0 + 6i| = \sqrt{0^2 + 6^2} = 6$\\I'm not sure how to find Theta.

ocean sealBOT
warm musk
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You need to find the theta in the geometrical form of $z^2$

ocean sealBOT
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Lilly (NasaExploration)

warm musk
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Aka you need to normalize the vector and identify your sinus and cosinus then solve

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So when you normalize you have $i$ because the norm of $z^2$ is $6$

ocean sealBOT
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Lilly (NasaExploration)

warm musk
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And then you will have $sin(2*\theta)=1$

ocean sealBOT
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Lilly (NasaExploration)

warm musk
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Then solve

heavy prairie
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I'm sorry but I can't follow that: I feel like I am lacking some really essential stuff, that, or people are just on a higher level of maths than I am at the moment.

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I also feel like the language barrier is a problem because I had my whole math education in Swedish

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I don't know what a geometrical form is

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Should I just envision a square?

warm musk
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Okay

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So let’s start from there

heavy prairie
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Yeah, would that be okay?

warm musk
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Actually let me pull up a whole talk I did about that form

warm musk
warm musk
# heavy prairie Yeah, would that be okay?

Firstly we will aim to explain what the trigonometric form of a complex number is. We will built it from the algebraic form you know

As you mean know, complex number are a thing (the only building element you need to know is that i^2=-1 which is weird but not too much if you think about it) and under their algebraic representation it looks like

z=a+ib

With a the real part and b the imaginary part. Noted :

Re(z)=a | Im(z)=b

You can also calculate the module of it :

|z|=sqrt(a^2+b^2)

This is a positive number and it would represent the length of the segment drawn between the origin of the complex plane and the actual point. You can easily realize that :

-|z|<=Re(z)<=|z| | -|z|<=Im(z)<=|z|

And therefore :

-1<=(Re(z)/|z|)<=1 | -1<=(Im(z)/|z|)<=1

What handy tool do we have to describe number between -1 and 1 ? We have trigonometric functions to do so. Therefore you can prove (here proving it is useless and likely out of your reach) that it exist a unique number theta in between 0 and 2 pi such as :

Re(z)/|z|=cos(theta) | Im(z)/|z|=sin(theta)

And this angle theta represent the angle between the segment drawn between the origin of the complex plane and the point AND the real axis (pointed toward the positive increment). Here I can’t really explain why as you don’t have the proof of it, it does explain a lot.

So you can write :

z/|z| = Re(z)/|z| + Im(z)/|z|i= cos(theta) + sin(theta)i

And us mathematicians can realize that writing e the complex exponential function such as :

z/|z| = e^(i times theta)

Makes a lot of sense as you can realize that it works nearly the same way as the exponential function. Every single property of it applies to this view of complex numbers (except a few exceptions). Here I won’t go into much detail as it’s just a bunch of trigonometric properties you need to demonstrate in a very painful way.

So you have to differentiate the classic and the complex exponential function. It’s for their relative closeness that we kept the same notation.

So now it’s as trivial as multiplying by |z| to find the trigonometric form of complex numbers. It’s called trigonometric cuz at its core there is trigonometric functions. So :

z = |z|e^(i times theta)

Please note that this definition don’t work if z=0 as you would multiply (and divide when building it) by 0 and therefore don’t guarantee the uniqueness of theta. So the trigonometric form of 0 is just 0.

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There a whole talk about it

heavy prairie
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Is that euler's formula?

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At the end

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z = |z|e^(i times theta)

warm musk
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We call it trigonometric form here because it uses trigonometric function

heavy prairie
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Okay I was confused about that

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But I could replace trigonometric

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with geometric

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here?

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So I get the geometric form of my complex number by rewriting it using euler's formula?

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My complex number being 0 + 6i

warm musk
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Yeah and you aim to find theta

heavy prairie
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ln(z) = iTheta * ln(|z|)

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ln(z)/(i*ln(|z|)) = Theta

warm musk
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No no don’t use ln

heavy prairie
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no

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okay

warm musk
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You can’t use it there

heavy prairie
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yes ok i uhh dont know how to do this then

warm musk
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You have to develop it

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With the sin and cos

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Okay so like

heavy prairie
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develop it ehhrrr

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yeah explain if you can

warm musk
heavy prairie
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Assuming I did everything correctly I would say so

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Looking at it, it still looks correct

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So I would say I found r

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Yes

warm musk
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What value did you found ?

heavy prairie
#

6

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oh yeah

warm musk
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Okay nearly there

heavy prairie
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and r is |z|

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i forgor

warm musk
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That r^2

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So you need to square it

heavy prairie
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no way

warm musk
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I mean root square it

heavy prairie
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6 isn't r?

warm musk
heavy prairie
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I never ended up using that formula

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I just want to get to use that formula

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Oh wait

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Oh you mean

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Now I use that formula

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and insert 6 into it

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r is 6

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but r^2 = 36

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typo

warm musk
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Okay @heavy prairie I am sorry but I am not really free right now

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Do you think we could talk about it in like 1 to 2 hours ?

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I will be able to help you more cuz I would want to talk about it from scratch instead of losing you like that

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Either here of DM I don’t mind both

heavy prairie
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I don't mind either way and yeah it can wait

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Don't feel forced to help though, only when you have time and want to

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I will close this in the meantime

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.close

lone heartBOT
#
Channel closed

Closed by @heavy prairie

Use .reopen if this was a mistake.

lone heartBOT
#
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After 15 minutes, feel free to ping <@&286206848099549185>.
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• Be polite and have a nice day!

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keen glade
#

How to solve for L ⁉️

lone heartBOT
cursive badger
#

It means, solve for l, in terms of w and P

keen glade
cursive badger
keen glade
#

Would I make the 2 cancel out the 2W?

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Or just leave as -2W + P/2

cursive badger
keen glade
#

Okay so thoughts on -W + P = L

cursive badger
#

How?

keen glade
#

What

cursive badger
#

I mean, if you are dividing both sides by 2, then the equation should be:
$-W+\frac{P}{2}=L$

ocean sealBOT
#

moaforlife

cursive badger
#

You have to divide P by 2 too

keen glade
#

Oh

#

Could you help with another one 😔

cursive badger
#

Yeah

#

Well that's what I am here for...

#

OK, WAIT!

keen glade
cursive badger
#

LET ME GIVE YOU THE INSIGHT

#

DO YOU KNOW WHAT EQUATION MEAN?

keen glade
#

Uh probably

#

It's when it has =

cursive badger
#

It means that there are 2 things which have the same value...

keen glade
#

And has a variable

cursive badger
#

And when we do any operation, we have to apply it to the whole...

#

Forexample

#

If we divided the right side by 2

#

then we have to divide the whole left side by 2

keen glade
#

I know but I forgot 😔

cursive badger
#

So that it remains an equation...

cursive badger
keen glade
#

So on the coffee question I have T = 5.50P +7F

#

What's it mean solve for F

#

And what would the constraints be

cursive badger
#

Like f=smt

#

And you have to manipulate what that smt is gonna be

keen glade
cursive badger
#

THEN?

#

you know what to do next...

keen glade
#

Divide

cursive badger
#

Yep

keen glade
#

But like

cursive badger
#

How?/

cursive badger
keen glade
cursive badger
#

yep

keen glade
#

From a

cursive badger
#

Nope

#

Otherwise, they would have mentioned it

keen glade
#

Oh alright I just thought it would use more numbers

#

And then for the constraints. Does it just mean that like he has to choose what he wants more of?

cursive badger
keen glade
#

Also thank you for the help

cursive badger
cursive badger
#

So, by constraints, probably they mean, what can be the maximum and minimum possible value of p and f, when T=40.

keen glade
#

Oh so like
"The max amount of coffee they can get is _"

cursive badger
keen glade
#

Is there any special way to solve the maximum value of P and F or do I just gotta mental math it kinda

cursive badger
#

If you read the question again, p is the cost of plain coffee and f is the cost of flavoured coffee

#

So, kind of:

#

"the maximum and the minimum value of both coffees that she/he can afford"

keen glade
#

So she can afford 5 flavored or like 7 plain

#

Like that?

#

Alright I gotta go, thanks again

#

.close

lone heartBOT
#
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cursive badger
#

My network is so bad... sorry I couldn't reply before...

lone heartBOT
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alpine sorrel
#

can sm1 solve this

lone heartBOT
alpine sorrel
#

<@&286206848099549185>

long axle
#

why dont u just do it

alpine sorrel
long axle
#

show ur work

alpine sorrel
#

let me explain wait

alpine sorrel
#

subtracted both

#

after that i got 4tanAcosA = m^2 - n^2

#

now i cant proceed

#

please help

gritty bramble
#

thats value of m^2 - n^2

#

now plug values of m and n in the rhs part (4sqrt(mn))

#

you'll get lhs = rhs

cursive badger
long axle
#

m^2 - n^2 = (tanA + sinA + tanA - sinA)(tanA + sinA - (tanA - sinA)) = (2tanA)(2sinA) = 4tanAsinA

long axle
gritty bramble
#

also yes, it should be sinA not cosA

alpine sorrel
#

wait let me do that as you told

#

yea i got it

#

ty @gritty bramble@long axle

gritty bramble
alpine sorrel
#

.close

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#
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lost abyss
lone heartBOT
lost abyss
#

How do i simplify this summation?

thorn monolith
#

Hmm i dont see how to simplify it but seems like you can split it to two sigma sums

alpine sable
# lost abyss

2 power n is summation of ncr coeff you can use that

#

and simplify

#

i did it

alpine sable
#

tell me if you dont understand anything

lone heartBOT
#

@lost abyss Has your question been resolved?

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lethal glacier
#

Doesnt matter, put 77 outside

gritty bramble
#

how are you "helper" (your role)

lone heartBOT
#

@full badge Has your question been resolved?

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austere shell
#

help zero

#

wow

lone heartBOT
austere shell
#

think i got part of it now sigh.

#

I was confused on this for a very long time regarding how this is equal, my new understanding is that no it isnt equal.

#

but that c/a is still apart of the equation even if it is removed(negative)

#

and that because of that when inputted into the quadratic formula it would undo the negative and give the result for the normal equation.

#

is this correct?

fresh wedge
#

Normal quadratic formula is
ax²+bx+c=0
Now if you divide everything by a you will have
x²+(b/a)x+c/a=0
Subtracting c/a both side will give you
x²+(b/a)x=-(c/a)

#

Where are you confused?

austere shell
#

they are deriving it btw

austere shell
#

well sort of

#

i understand how they did this not how its possible

#

people tell me this is somehow equal to the original polynomial

#

but if polynomials are a bunch of components that make up the behavior of a parabola

#

wouldnt removing c/a alter that behavior

#

yes -c/a is still there on the other side but its negative

#

would that not then alter the behavior causing the parabola to be more flat or go in a negative direction since negative value was subtracted from the answer?

#

or by equal do they just mean when you solve it out via the quadratic formula it would become equal afterwords because the formula would undo it and generate the original quadratics answer?

fresh wedge
#

Yes if you alter anything in parabola equation

#

It will change the graphs

austere shell
fresh wedge
#

But solving a quadratic equation is a different topic than seeing parabola, graphs finding major minor axes etc

fresh wedge
austere shell
#

what are major and minor and how are they different dont you need the zeroes to find a parabola?

fresh wedge
#

Idk the exact term to define them

#

The general formula for a parabola is y = a(x-h)² + k or x = a(y-k)² + h, where (h,k) represents the vertex

#
ax²+bx+c=0```
#

If you consider y=0, then parabola equation will change into a quadratic equation yes

#

Or x=0 for 2nd parabola formula

austere shell
#

define Y

#

also define H and K

#

(their representations and meanings)

#

when graphing this what values would be assigned to X and what to Y (axis)?

lone heartBOT
#

@austere shell Has your question been resolved?

#
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tight thunder
lone heartBOT
tight thunder
#

Guys this matrix would be

#

2-parameter solution?

#

i often read 1 parameter solution

#

2 parameter solution

#

but dont know what mean

#

it means this?

#

because of the 4th coloumn having unknowns which are not on the main diagnal?

#

.close

lone heartBOT
#
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alpine sable
#

Functions f and g are defined from A to A, where A is a non-empty set.
If f(g(x) function is one-to-one which of the following is absolutely correct?
A)f is surjective B)g is surjective C)f is one-to-one D)g is one-to-one E)g(f(x)) is one-to-one

A video solution says:
If f(g(x1))≠f(g(x2)) then g(x1)≠g(x2) so g is one-to-one
But I didn't understand how other options can be false

lone heartBOT
#

@alpine sable Has your question been resolved?

alpine sable
#

<@&286206848099549185>

valid trout
#

Because it doesn't necessarily mean that every element of A is covered

#

So that's A and B gone

#

I am not sure I fully agree with the solutions

#

We can say that g(x1) = y1 and g(x2) = y2 and assuming that f(y1) is different from f(y2) it means that y1 is different from y2

#

Meaning that f is one-to-one

#

However with this information we don't know anything about g and thus we can't conclude E is true either

lone heartBOT
#

@alpine sable Has your question been resolved?

alpine sable
lone heartBOT
#
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woven plaza
#

Is this proof correct?

lone heartBOT
#

@woven plaza Has your question been resolved?

woven plaza
#

<@&286206848099549185>

lone heartBOT
#

@woven plaza Has your question been resolved?

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waxen turtle
lone heartBOT
waxen turtle
#

idk what classifies as each

#

someone plz tell

lone heartBOT
#

@waxen turtle Has your question been resolved?

waxen turtle
#

<@&286206848099549185>

potent owl
#

Is it 3-6 or all problems

waxen turtle
potent owl
#

Do you understand the difference between jump and infinite

waxen turtle
solar narwhal
solar narwhal
#

You can see it's constant for some time then it suddenly jumps upto 1 at 1

waxen turtle
#

idek how to find that

#

is that like piecewise

solar narwhal
waxen turtle
#

yes

solar narwhal
#

Then take the Right hand limit and the left hand limit

#

If they're different then there exists a jump on that point

waxen turtle
#

and wat is removable and non removable discontinouty

#

i forgor

solar narwhal
#

,w plot absolute value of 1/x

#

Here at x=0

#

Function shoots upto infinity

waxen turtle
#

am I doing like limits or sum idk it doesn't say lim

solar narwhal
#

BUT

#

The value of the function is not defined or different than limit

waxen turtle
#

wat does that mean

#

wats a rhl

#

and lhl

solar narwhal
solar narwhal
waxen turtle
#

o

#

ok the first one

#

i have no idea

#

do I test points around 3

#

idk

solar narwhal
solar narwhal
waxen turtle
#

1/(x-3)^2

#

idk

solar narwhal
waxen turtle
#

x=3 is prob important

solar narwhal
#

Take the RHL and LHL at 3

waxen turtle
#

right hand limit it goes to infinity

solar narwhal
waxen turtle
#

si does left

#

so

solar narwhal
#

It's infinite

#

Do you understand why?

waxen turtle
#

Ya

#

wat if one goes to neg infinity

#

or both

#

wat would it be theb

solar narwhal
solar narwhal
#

There's a jump or more accurately a asymptote

waxen turtle
#

do I need anything else for 1

#

or do I just write infinity

solar narwhal
waxen turtle
solar narwhal
waxen turtle
#

is it a removable discontinuing or no

#

cuz both go to inf

#

same

solar narwhal
waxen turtle
#

wait wat is a normal disconiouty

#

idrk anything Abt continuity tbh

solar narwhal
#

Removable would mean that we can define the function to equal the RHL and LHL so that it becomes continuous

solar narwhal
#

Or there are no 'holes'

waxen turtle
solar narwhal
#

It's a example of discontinuity at every integer

waxen turtle
solar narwhal
#

Can you try the second one?

waxen turtle
#

okk

#

remov disc on 4 right

solar narwhal
solar narwhal
solar narwhal
#

No

#

It's continuous on

#

4

waxen turtle
#

ruh roh

#

i think i sold on my qui

#

quiz

#

on this

#

today

#

💀

#

i def said something like that was a remov disc

solar narwhal
waxen turtle
#

😭

#

i took it today

#

earlier

#

anyways

solar narwhal
#

I don't think my brain is functioning properly

#

I just woke up

solar narwhal
#

Anyways

#

There's another point you'll have to check

waxen turtle
#

is it a remov disc or wat

solar narwhal
#

There are 2 points

waxen turtle
#

heudhshsh

solar narwhal
#

Where we check

waxen turtle
#

5

solar narwhal
solar narwhal
solar narwhal
waxen turtle
#

light work

#

i never lose

solar narwhal
#

Check on 5

waxen turtle
#

ok from pos direction it's inf

#

neg inf from neg

solar narwhal
#

Yeah

#

So it's non removable discontinuity since

#

They're different

waxen turtle
#

okii

solar narwhal
#

Try third

waxen turtle
#

OK

#

idk

solar narwhal
waxen turtle
#

idk how

#

like

#

idk

#

idek how to solve absolute value functions

#

I was never taught

solar narwhal
#

Those are the points we care

#

Recall

#

That Abs Value of x is x itself for x>0

#

And -x for x<0

waxen turtle
#

help

solar narwhal
#

So solve for when the function is positive or negative

solar narwhal
waxen turtle
#

so like

#

-x-2

#

idk

solar narwhal
#

Abs(x) = { x for x>=0,
-x for x<0

#

So

waxen turtle
#

wat does abs mean

solar narwhal
#

Abs( x+ 2 ) = { x+2 for x+2 >=0
-(x+2) for x+2<0

solar narwhal
waxen turtle
#

do I make a version where x is neg

#

like -x+2

waxen turtle
#

oh the whole thing

solar narwhal
#

Solve the inequality in there

waxen turtle
#

do I include the bottom

solar narwhal
#

That'll be the condition on x for the function to be x+2 or -(x+2)

waxen turtle
#

or liek forget it

solar narwhal
waxen turtle
#

like

#

nvm

waxen turtle
#

so 4 and -4

#

idk

solar narwhal
solar narwhal
waxen turtle
#

😮‍💨

solar narwhal
#

The inequality is x+2<0

waxen turtle
#

OH

solar narwhal
#

Subtract 2 from both sdes

waxen turtle
#

WAIT

#

i thought it was

solar narwhal
#

Do the other one similarly

waxen turtle
#

x+2>=0

solar narwhal
#

Both are pieces of the same function

waxen turtle
#

I'm uhh

#

i got

#

x >= 2

#

and x>2

#

😭

solar narwhal
solar narwhal
waxen turtle
#

oh

solar narwhal
#

You subtract 2 from both sides

#

So -2

waxen turtle
#

-x-2<x

#

-x<2

#

x>-2

solar narwhal
waxen turtle
#

but they r like the same thing

solar narwhal
#

Do the other one too

solar narwhal
waxen turtle
solar narwhal
waxen turtle
solar narwhal
#

No

#

The inequalities are

#

x+2 >=0

#

And

#

x+2<0

waxen turtle
#

oh

#

okkk

solar narwhal
#

Solve those

waxen turtle
#

x<-2

#

so like that includes everything

#

Fr

solar narwhal
solar narwhal
waxen turtle
#

plus the other thingy

#

it's everything fr

solar narwhal
waxen turtle
#

oki

#

now wat

solar narwhal
#

Now write the function as piecewise

waxen turtle
#

idk how

solar narwhal
#

For x less than -2

#

Abs(x+2) = -(x+2)

#

So open the initial function like this

waxen turtle
#

IDK

solar narwhal
#

What's the function

waxen turtle
#

-x-2 for x<-2

solar narwhal
waxen turtle
#

and x+2 for x≥2

#

is that the piecewise

solar narwhal
#

So I ask you again

#

What's the initial function

waxen turtle
#

omg

#

do I divide both of those by x+2

solar narwhal
waxen turtle
#

EZ

solar narwhal
#

Now what's the resulting piecewise function

waxen turtle
#

OK

#

1 for x ≥ -2

#

-1 for x < -2

solar narwhal
#

Yeah

#

Take limit at 2

waxen turtle
#

1

solar narwhal
waxen turtle
#

don't u just plug it in

solar narwhal
waxen turtle
#

it's greater than -2

#

so it's 1

solar narwhal
#

Take limit

waxen turtle
#

how

solar narwhal
#

RHL and LHL

waxen turtle
#

it's a straight line

#

at 2

solar narwhal
waxen turtle
#

liek a month

solar narwhal
#

Bro just take the RHL and LHL they're different

waxen turtle
#

ISNT IT A STRAIGHT LINE???

solar narwhal
waxen turtle
#

at 2.1 it's 1

#

and 1.9 it's 1

#

???

solar narwhal
waxen turtle
#

how i

#

it's not less than -2

#

so it doesn't count for that one

solar narwhal
#

Ohh

#

-2 please

waxen turtle
#

.

#

ok

#

it's a jump

solar narwhal
#

.

solar narwhal
waxen turtle
#

jump at x=-2

#

right

solar narwhal
waxen turtle
#

it's non remov right

#

idk

solar narwhal
#

Try the next one

solar narwhal
waxen turtle
#

i have to go tho

#

sooo

#

rip

#

😔

#

.close

lone heartBOT
#
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After 15 minutes, feel free to ping <@&286206848099549185>.
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trail imp
#

I wanted to know which one of the steps is wrong here. The correct answer is 1/6.

ocean whale
#

,rotate

ocean sealBOT
trail imp
#

Yes, in the first step

ocean whale
#

Your derivative of the numerator looks wrong

trail imp
#

I used sinx/x = 1 to delete the sin from sin(sin x)

ocean whale
#

I'm saying your derivative of cos * sin - cos is not correct

trail imp
#

What would be the correct derivative?

ocean whale
#

Well, you'd use product rule for cos * sin, correct?

trail imp
#

But it is not cos * sin, the angle of cos is sin x

ocean whale
#

Oh my bad

#

I misread that

trail imp
#

Np

ocean whale
#

That derivative is still incorrect, you'd use chain rule

#

Wait

#

I just can't read

trail imp
#

That just made me laugh

#

This solution was given for this question.

#

Oh, got it

#

Sin(sinx)/sinx wouldnt equal to 1 bcoz it is x tending to 0, not sin x tending to 0

#

But isn't it the same thing?

lone heartBOT
#

@trail imp Has your question been resolved?

lone heartBOT
#
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After 15 minutes, feel free to ping <@&286206848099549185>.
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unreal pawn
#

Who could graph the quadratical function: f(x) = -(x+3)^2+4?

trail imp
lone heartBOT
#

@unreal pawn Has your question been resolved?

unreal pawn
#

yes, a parabola. Correct?

trail imp
#

Exactly

#

So, what is the standard equation for a parabola?

unreal pawn
#

f(x) = a(x+p)^2+q

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-p I mean

trail imp
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Yep

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So, when it's -a, it just means that it's an upside down parabola

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And you can substitute x values to find the corresponding y value to graph the parabola

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Tho, there's a really great website for it. Search up desmos graphing calculator

unreal pawn
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i am asked to graph it, using the given formula. I did use graphing calculators, its just kinda unclear to me why it resulted in a -1 x-intercept

trail imp
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Oh, you can just substitute the value of y = 0 and find the x intercept

unreal pawn
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wdm

trail imp
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By y, I mean f(x)

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Function of x is 0 on x intercept

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I am so used to throwing around y's in place of f(x) to make the question easier, I didn't realize that it's not even a variable here

lone heartBOT
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small badge
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Need Linear Algebra help; I've tried this homework problem a few different ways and still getting it wrong.

hushed locust
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i would try reversing s and t

small badge
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wouldn't s represent x3 and t represent x4?

hushed locust
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hmm didn't work but I'll ask my professor tomorrow morning, thank you though!

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trail imp
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My answer here seems to be wrong. The correct one is 1/6. Where is the mistake in the solution?

unborn plover
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,rccw

ocean sealBOT
gritty bramble
trail imp
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I used sinx/x =1

modern kernel
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sin(sin x) became sin x

modern kernel
gritty bramble
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you cant do that

modern kernel
trail imp
gritty bramble
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firstly

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where did u get sinx/x from

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u didnt split the denominator

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even if u do

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its sin(sinx)

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not just sinx

trail imp
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well, I have sin(sinx). so, I multiplied and divided by sinx and got sinx

gritty bramble
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what

gritty bramble
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in your work, sin(sinx) became sinx out of nowhere

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if u diviied by sinx, wheres the sinx in denominator?

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also the x you took out of 4x^3, its still 4x^3 instead of 4x^2

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in short its all wrong

trail imp
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no, like sin(sinx)*sinx/ sinx

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so, sin(sinx)/sinx would become 1

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and sinx would remain

gritty bramble
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oh

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but the problem is

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you dont put limit in between like that

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its affecting the whole function here

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the numerator has another term in addition

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you cant do what you are trying to do

trail imp
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but dont limits have additive propertry?

gritty bramble
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what

trail imp
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like if you have lim x tends to 0 (x+y), you can put it as lim x tends to 0 x and lim x tends to 0 y

gritty bramble
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(x+1)x^2, if i multiply and divide by x, as in x*x/x, then cancel out the x^2 in numerator and denominator, this just changes the whole function

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infact all these ^ steps are wrong

trail imp
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i see. then, do I have to lhopital all the way or is there any other way I can do this question?

gritty bramble
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u just multiplied by sinx/sinx (that too wrong)

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if u have (x+1) and you multiply by x then the its x(x+1) not x^2 +1

trail imp
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yeah, i splitted and recombined them.

gritty bramble
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if u split them already then you dont combine them back

trail imp
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but why?

gritty bramble
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because you changed the split part

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it just changes the whole function completely

trail imp
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yeah but the denominator and the limit is still the same

gritty bramble
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but the function is changed

trail imp
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yeah, but according to the addtive property why does that matter

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if the limits are same, I can add them

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my basics do suck real bad so, I really need to clear these doubts

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this was the solution provided for the question

gritty bramble
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because using lhopital it will get complex

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since you will have to keep differentiating until the indeterminate form goes away (so 4 times)

gritty bramble