#help-36

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carmine plaza
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literally

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like i want a rigorous understanding

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i dont understand

steady locust
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the first is the indefinite integral, its the anti-derivative. the second is the definite integral, it computes to a number

carmine plaza
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seems vague

steady locust
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the anti-derivative is the inverse of the derivative, its a function. the definite integral is the area under the curve

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$\int{f(x)}dx$ = anti-derivative of f(x), $\int_a^b{f(x)}dx$ = definite integral of f(x) from a to b

carmine plaza
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i mean the derivative represents a tangent line

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the integral represents the area under the curve

soft zealotBOT
carmine plaza
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if its indefinite it just represents the entire area under the curve at any given point

steady locust
carmine plaza
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but that function is still an area

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it represents an area

steady locust
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not really, because it depends on where you start for the area under the curve, thats why the indefinite integral has + C

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have you learned doing indefinite integral / antiderivative?

supple jolt
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The indefinite integral just gives you a function that you use to compute the area

carmine plaza
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right

steady locust
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yeah, but you need to compute over an interval, not just at a value

supple jolt
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I mean you can go from a to a

carmine plaza
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hm

supple jolt
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But yes

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I suggest watching a youtube video about this

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Its kinda hsrd to explain over text

steady locust
carmine plaza
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i guess its not rly something that matters

supple jolt
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Visuals help

carmine plaza
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i dont need to necessarily know this

steady locust
carmine plaza
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so if an integral doesnt have bounds it cant be improper

supple jolt
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Do you have like a specific question or just want to know what integrals are in general

steady locust
steady locust
carmine plaza
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i just didnt understand that difference

spring haven
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Indefinite integrals aren’t real

steady locust
carmine plaza
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yeah

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idk

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well

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is he wrong idk

spring haven
carmine plaza
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i feel like thats true XD

spring haven
supple jolt
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Definite and indefinite?

carmine plaza
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like thats why i was confused i always assumed it was shorthand for an improper integral between -inf to inf

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that indefinite was

steady locust
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you just confuse people

carmine plaza
steady locust
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they are related by the fundamental theorem of calculus

carmine plaza
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yeah i understand now

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indefinite is just like abstracted away from application

supple jolt
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If they are bounded the reuslt is a number

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Of they are unbounded the result is a function

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Think of it this way

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For now

carmine plaza
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alr everything else makes sene

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ill open something else if i have another question

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.close

final saddleBOT
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Channel closed

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supple jolt
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Right

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Just watch a youtube video

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If you want

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Its easier to understand

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Your choice

carmine plaza
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i understand i mean that wasnt the issue

supple jolt
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All right

final saddleBOT
#
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last forum
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short question for example if im trying to solve
-3 -1/5 am i supposed to multiply or not

jagged flare
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$-3-\frac{1}{5}$

soft zealotBOT
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ihave<skissue>

jagged flare
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this?

last forum
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yes

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i asked chatgpt and it kept going back and fourth not knowing if the right way was to not multiply or to multiply

jagged flare
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thats a subtraction, -3 then subtract a fifth

final saddleBOT
tired walrus
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anyway -3 - 1/5 is quite clearly a subtraction of 1/5 from -3

last forum
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i say i use it personally

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for like

tired walrus
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don't be surprised if math turns out to be 17 years of great pain and suffering.

last forum
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explanation

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its pain and suffering now lol

last forum
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full question btw

tired walrus
tired walrus
# last forum

ok so you do in fact subtract 1/5 off both sides here and you end up with x/3 = -16/5

last forum
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i usually do it with steps

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i cant rlly do it mentally

tired walrus
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ok, so do it with steps.

last forum
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1 sec

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ill send screenshot

tired walrus
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i am telling you very slightly in advance what will happen

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you can check yourself against me -- if you arrive at the same answer as me, it means you made an even number of mistakes

last forum
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ignore messy drawing i hate mouse

tired walrus
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the -3.2 bit is ok

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then you divided by 1/3 on the left (also good), but... subtracted 3 on the right?

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you were meant to multiply by 3 on both

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the golden rule is you do the SAME THING on both sides

last forum
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i think i subtracted because it was positive and i moved it over so its negative

tired walrus
last forum
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its just so i can visualize it better

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moving over making it negative yk

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thats why im crossing out

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chatgpt mightve corrupted me

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if a fraction has a - in between you can still multiply?

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😵‍💫

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actually i get it

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i was dividing it not subtracting it so theres no need for it to be negative

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smh

final saddleBOT
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@last forum Has your question been resolved?

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tiny kraken
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Let A be a set containing n elements .A partition of a set is a set of k non-empty subsets such that
$$A = A_1 \cup A_2 \cup A_3 \cup \dots \cup A_i , ( A_i \cap A_j = \o , \forall i,j = 1;2;\dots ;k )$$
For example: $B={a,b}$ has 2 partitions ${{a},{b}}$ and ${{a,b}}$ \

How many partitions of a set with 4 elements $C={a,b,c,d}$ are there?

soft zealotBOT
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Fionna The Unemployed

rugged merlin
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What have you tried

silver dew
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There is a recursion formula for the Bell number. You can use that

tiny kraken
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Okay so, I was able to do this problem using recurrence but I couldn't find a closed form or at least non-recursively relationship

tiny kraken
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Is it like

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$A_k = A_{k-1} + \binom{n}{1} A_{k_2} + \dots$

soft zealotBOT
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Fionna The Unemployed

hasty mist
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The Bell number is the sum of all Stirling numbers of the second kind

silver dew
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You can easily deduce it, by choosing some k elements as the last set, and n-k elements have their own division:

tiny kraken
silver dew
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$B_{n+1}=\sum_{k=0}^{n}\binom{n}{k}B_{k}$

soft zealotBOT
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Cogwheels of the mind

tiny kraken
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Ehh but I failed

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So it's called bell numbers?

silver dew
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Yeah

tiny kraken
silver dew
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Sorry, I am going to reformulate the thought again:

hasty mist
silver dew
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Dividing the {1,2,…,n+1} is the same as choose n-k elements from {1,2,…,n}, along with n+1 to make a subset, and B_k many ways to divide the remaining of {1,2,…,n}. For k=0,1,…,n

hasty mist
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[ rb{ B_n = sum_{k=0}^n S(n,k) }]

soft zealotBOT
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クーリー

tiny kraken
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What I did was, choose an element m from the set A then doing cases work, if m standalone then it has the amount of partitions of a set with 3 elements ways and so on

tiny kraken
silver dew
tiny kraken
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But how can I find something that's non-recursive form

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Does it have one?

silver dew
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?

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It is recursive

silver dew
tiny kraken
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I know

silver dew
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B_1=1, good to go.

tiny kraken
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I mean, like how Fibonacci numbers also have a closed form

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Does bell numebers have one?

silver dew
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I don’t think so

hasty mist
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Yeah,

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Dobinski

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It’s not very practical though

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[rb{B_n = frac1e sum_{k=0}^{oo} frac{k^n}{k!} }]

soft zealotBOT
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クーリー

hasty mist
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It follows from the fact that a Poisson(1) random number of labels produces partitions with expected count exactly equal to the Bell number.

tiny kraken
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hmmcat hmm

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Okay thank y'all

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That's my only question

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Is this like a university thing

hasty mist
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Yes

tiny kraken
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Okay I'm still a highschooler

silver dew
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The last thing he mentioned probably is. Beyond that no, all elementary

hasty mist
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You seem unemployed

tiny kraken
hasty mist
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I knew it

silver dew
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But if you are interested in combinatorics in general you can always read enumerative combinatorics by Stanley. It’s beautiful

tiny kraken
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I'll give it a try, the exam I'm going to take are full of combinatorics problems

silver dew
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If you have an exam ahead then don’t mind. I meant a hobby kind of thing in free time

tiny kraken
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Thanks y'all

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.close

final saddleBOT
#
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final saddleBOT
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spring abyss
#

about multivar differentiation chain rule, does wuu = wxx * (xu)^2 ?
since d^2w/dx^2 needs to * dx twice and / du twice if treating them as numbers on simple arithmetic

main mirage
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When in doubt - you can always take derivatives manually!

main mirage
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Is w a function of x, and x depends on u?

spring abyss
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lets just say, wu exists, wx exists, and xu exists

main mirage
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Like

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w = w(x)?

spring abyss
main mirage
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Okay so w is a function of x and t, since its the wave equation.

main mirage
# spring abyss idk

So here's the deal.
We want to write w, a function of x and t: w(x, t) into w a function of u and v w(u, v), and namely its derivatives as well. (The reason being is because the question wants us to substitute u and v in place of x and t)

What does the multivariable chain rule say about taking the derivative? I.e
If
w = w(x, t)
How do we figure out what dw/du is?

spring abyss
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wu = wx * xu

main mirage
# spring abyss wu = wx * xu

Mmmm unfortunately not :(
The problem is that u depends on both x and t, so this equation is actually missing something.

spring abyss
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i gotta check my notes i kinda forgot how this works now

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wu = wx . xu + wt . tu

main mirage
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Good! Because u depends on x and t, you are effectively doing the chain rule for each variable.

spring abyss
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then another question, how to expand this concept onto 2nd d?
wxx = wuu . uxx +...
or wxx = wuu . (ux)^2 +... ?

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wait

main mirage
spring abyss
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wxx = d/dx(wx) where i gotta expand both d/dx and wx?

main mirage
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That means you have to apply the multivariable chain rule to wx * xu and wt * tu separately, which is not as easy algwbraically as it might seem.

spring abyss
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wx has its own expression, then d/dx becomes d/du . ux + d/dt . tx

main mirage
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Yeah, but like

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You dont actually need to find what wx is :)

spring abyss
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wuh

main mirage
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As a hint, the strategy for this question only requires you to find wuu and ||wtt||.

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If you can find those two, you can solve the question :)

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Well actually

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You dont even need to find those two

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The question tells you exactly which derivative you need to find.

spring abyss
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Hmm

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I’ll look into it later then

main mirage
spring abyss
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Thx

main mirage
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What derivative do you think you need to compute?

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(Anyway take a break if you need it :)

spring abyss
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Yeah I gotta have dinner rn

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Bye

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final saddleBOT
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final saddleBOT
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languid bay
#

how do you solve this? I made it into a quadratic equation, solved for a in 2 diff values like a = -3 and a =1 , and I substituted the a values for both the equation, I get 9 and 809/27. however the answer is 71/27 is there anywhere I'm going wrong

smoky bramble
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do you know the factorization of a^3-b^3?

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if yes, you should be able to factorize a^3-1/a^3

languid bay
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not very sure, but like how do you apply it?

smoky bramble
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3a-3/a=3(a-1/a)

languid bay
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and you solve for a? or do we like directly substitute it in?

smoky bramble
main mirage
languid bay
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can we not substitute a-1/a into the second equation?

main mirage
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As d1 implicitly mentioned, you are basically just doing some neat substitution tricks.

smoky bramble
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why not?

languid bay
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so in that case I can take the value to be -4/3 and solve?

smoky bramble
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a-1/a?

languid bay
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yess

smoky bramble
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yeah

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just solve

languid bay
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okk

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I got the answer, tyy

smoky bramble
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the easiest way is to recognize the expansion of (a-1/a)^3

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-3(a-1/a)

languid bay
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ohh

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.close

final saddleBOT
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final saddleBOT
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tranquil charm
#

how to calculate Z-transform of n/n! ?

final saddleBOT
tranquil charm
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i know that Z-ransform of 1/n! is e^{1/z}

trail mango
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what’s another way to write n/n! that looks similar to 1/n!

trail mango
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yep

tranquil charm
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alright but what now?

trail mango
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let me see…

tranquil charm
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nvm i got it from definition

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but thanks for help! greatly appriciated

trail mango
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yea i think it should just shift nicely

tranquil charm
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.close

final saddleBOT
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tranquil charm
#

how to calculate $\mathcal{Z}$-transform of $\ln\left(\frac{z-1}{z}\right)$?

soft zealotBOT
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Slowaq

tranquil charm
#

.close

final saddleBOT
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final saddleBOT
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scenic nest
#

I am trying for an optimized Gaussian elimination, should I only stop when var=number and at the end? I have so far implemented ranking where the first variable is, is like var=number and the first variable in the diagonal being the thing to subtract from the next rows enough or should I full sort?

scenic nest
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Note this is parallel on the GPU. X E.

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I also have implemented the stop. X E.

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Is this better with or without sorting the rows?

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Should I just continue implementing and see if the not sort can work?

vital crag
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if you don't need to perform an operation, why would you need to

scenic nest
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Oh, is it possible to just not even use a maximum?

vital crag
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what runtime are you aiming even aiming for. "optimized" is ambiguous

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O(n^3) ?

scenic nest
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Yeah, at worst O(n^3), is there something better I should consider?

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Just as optimized as I can make it. X E.

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Just fastest I can make it with minimum extra storage. X E.

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Thanks for talking. X E.

vital crag
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In mathematics, Gaussian elimination, also known as row reduction, is an algorithm for solving systems of linear equations. It consists of a sequence of row-wise operations performed on the corresponding matrix of coefficients. This method can also be used to compute the rank of a matrix, the determinant of a square matrix, and the inverse of an...

desert mantle
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there are highly highly optimized versions of gaussian elimination available

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why would you want to code it yourself

drowsy epoch
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exactly...

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ig u r just wasting time

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unless u wanna really learn/study it

desert mantle
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nothing you can produce will come close to what others have done

drowsy epoch
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exactly... hard pillow to swallow

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as a programmer

scenic nest
scenic nest
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Thanks for talking. X E.

desert mantle
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any useful language should have a linear algebra library available

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which has gaussian elimination already implemented

scenic nest
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Those... open source? How easy are those to glean from?

vital crag
scenic nest
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I already have a basic understanding of matrices. X E.

desert mantle
vital crag
scenic nest
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I am finding a lot of CPU gaussian elimination, any GPU?

vital crag
tepid ridge
scenic nest
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Come on internet, GPU parallel non-square. X E.

drowsy epoch
tepid ridge
drowsy epoch
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o oki

vital crag
#

your mom must have installed discord for you

tepid ridge
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do not claim ticket if you do not know how to solve

vital crag
#

ask your mom to explain to you how discord works next

vital crag
scenic nest
tepid ridge
vital crag
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read

tepid ridge
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I will do that once I arrive home

vital crag
tepid ridge
#

next are you gonna use ai?

scenic nest
scenic nest
tepid ridge
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anyway I have to go

tepid ridge
scenic nest
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Well, is there another place to look other than GitHub?

desert mantle
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google...?

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how about you actually look

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but serious question, do you actually need this whole completely optimized shit. or are you just gonna use it to solve 10x10 systems

scenic nest
vital crag
scenic nest
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I spent most of today and also exhausted GitHub. X E.

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Codeberg turns up no entries. X E.

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Maybe I am just bad at searching?

vital crag
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you need specific search terms

scenic nest
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And it can't be like use our algorithm, it must be like look at ours, feel free to copy. X E.

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Nothing is in Slang shaders now so if nothing else I will at least translate. X E.

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But the no pivot solver gives me hope. X E.

faint edge
scenic nest
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Anyway, back to the original question, do I need sort or just like put the frontmost variable equation up top to zero out the rest?

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I would think any extra work will degrade performance. X E.

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Should I just try myself and later ask why it does or does not work?

vital crag
scenic nest
scenic nest
scenic nest
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I read some. X E.

molten ginkgo
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Do u guys know someone's explaining How to solve a linear programming problem using the graphical method?

molten ginkgo
molten ginkgo
quasi rapids
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This help channel is occupied

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If you have your own question, make your own help channel

molten ginkgo
scenic nest
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Well, going through the given link, it does not actually have algorithms, just a use our system ad. X E.

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If you can find the repo form great. X E.

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And something slow is better than nothing, without an example code, it is nothing. X E.

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What? Second to last channel down?

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Anyway, either provide an example I can copy or answer the pinned question please?

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And all numbers are real. X E.

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This is also 4d+. X E.

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What does finding a no pivot one mean?

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Hi, welcome. X E.

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What is a pivot in Gaussian elimination?

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I know, I should just look it up. X E.

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Oh, the top row that is setting others zero is the pivot. X E.

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That no pivot is just wrong. X E.

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AI says I can, but blah, AI. X E.

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I think just place any first place should work, and don't interfere with solutions should work. X E.

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I would almost thank people here if this had come from anyone else. X E.

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GPU gaussian elimination is scarce. X E.

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I am modeling it on the CPU in Rust. X E.

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At least on CPU I know like line. X E.

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Any other Gaussian elimination tips?

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I think this can work. X E.

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Okay, I think this goes in stages, like first set ranks and go for maximum, search for singles, if found then substitute, next set matrix with below top one only, a thread per each element subtracting except the first which stays the same and is needed, then check for single variables, then set that to zero unless single, if single found, use it. Could this be more optimized? X E.

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After the set up matrix repeats. X E.

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Maybe I should have a single vector like thing of found variables and zero out singles. X E.

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So rank->move up one->eliminate one->check singles and place in vector->zero out not singles->start. X E.

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Rank can be done parallel per equation with end at first, move up one can be done with a single swap single thread, eliminate one big number of threads, check singles per equation, maybe a next step to move that variable to equals side per equation between, then zero it out in the equations, then start. X E.

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Is this efficient or trash 🗑️?

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Also the startup is like rank, move up one input, set up matrix not including that index, check and substitute in singles, start. X E.

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Also, I should probably have like if absolute value less than some epsilon then zero. X E.

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Oh, and also, may as well stop the single variable checker at second variable and if one contains zero variables and last element like after equals is not zero then atomically set a variable, then at the end of the iteration a checker moves it to non-volatile memory, every thread checks that before continuing on the GPU. X E.

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I could probably have just addition and if integer=0. X E.

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Should I just implement and stop bothering you?

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Simplicity wins I guess. X E.

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I don't need this any more, thanks for trying all. X E.

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.close

final saddleBOT
#
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dawn zealot
#

So I'm a calc BC student and I have an epsilon-delta proofs test for continuity and limits. I am 67% sure there will be 3 questions (which are proofs) and 40 minutes at most to finish them. I'm okay with solving them but the teacher told us that at least one of the problems will require proving either the squeeze theorem, uniqueness of limits, or the limit law involving the composition of limits. I know how to prove the squeeze theorem but I hae no idea how to do the other 2 (although I guess that the uniqueness one might involve contradiction). Can someone please help me? My test is tomorrow.

opal pelican
dawn zealot
#

Thank you!

opal pelican
#

Alright, so, as you might've guessed, we'll prove this by contradiction

dawn zealot
#

Okay

#

So is our objective here to prove that if lim x->a f(x)=L and lim x->a f(x)=M then L=M?

opal pelican
#

Essentially assuming there exist two distinct limits and showing they'll be the same, the idea is that if the function converges to both limits, then it is within distance epsilon of each limit for distances lesser than certain δs, we'll choose a δ small enough to be within both of these ranges, and since this can be done for any ε>0, both limits will be arbitrarily close to each other

dawn zealot
#

Okay. How would I proceed beyond this?

#

Would I suppose instead that L does not equal M

opal pelican
dawn zealot
#

Then would I use the epsilon-delta definition of limits on each of the functions separately and assign a delta_1 and delta_2?

opal pelican
#

Which is easy knowing the solution, not so much if you don't

dawn zealot
#

So would we work backwords to find epsilon?

opal pelican
#

Mainly because without some chosen epsilon "you have nothing"

dawn zealot
#

How would I proceed beyond this then?

opal pelican
#

You can't choose deltas and as such cannot exploit the limit condition

dawn zealot
#

ok

#

What should I use for the epsilon then?

opal pelican
#

The idea for this particular choice is that we want something smaller than the distance between the limits

#

That is, something positive but smaller than |L2-L1|

#

For convenience, and without loss of generality, assume L2>L1

dawn zealot
#

Okay

#

So would epsilon be less than |L2-L1|

opal pelican
#

That is, say ε=something

dawn zealot
#

Epsilon = L2-L1?

opal pelican
#

What ways do you know to reduce the value of something while keeping it positive?

dawn zealot
#

Triangle inequality?

opal pelican
#

So won't give you a valid choice of epsilon

dawn zealot
#

Greater denominator?

#

Lesser numerator?

opal pelican
#

L2-L1 is not a fraction though?

dawn zealot
#

Ok

#

I have no idea

opal pelican
#

Dividing by integers

#

(L2-L1)/n ≤ (L2-L1), strict for n>1

#

And that doesn't change the sign

dawn zealot
#

Oh okay. Would I choose some random interger?

opal pelican
#

In general, when you want to find a positive value lower than another one you're given, dividing by some positive integer should be your go to choice

opal pelican
dawn zealot
#

okay

opal pelican
#

As if you choose (L1-L2)/2, L1+ε and L2-ε will "almost overlap"

dawn zealot
#

Would 3 work?

opal pelican
#

Picture it as a line segment separating them both, of length |L1-L2|

opal pelican
#

The one I chose as well

dawn zealot
#

Thank you

opal pelican
#

So well, now you have your ε, (L2-L1)/3

dawn zealot
#

Would this epsilon be for both |f(x)-L1| and |f(x)-M|

opal pelican
#

And you'll need your deltas for this chosen epsilon

dawn zealot
#

Am I allowed to use the epsilon for both of them or do I have to explain/justify this

opal pelican
#

The definition states something happens for any choice of epsilon

dawn zealot
#

Okay

opal pelican
#

So it in particular will work for that choice of epsilon, in both cases

dawn zealot
#

So with that epsilon, what should I do?

opal pelican
dawn zealot
#

|f(x)-L1|<(L2-L1)/3 and |f(x)-M|<(L2-L1)/3

opal pelican
dawn zealot
#

|x-a|<delta_1, |x-a|<delta_2

opal pelican
#

The whole thing is:
∃ (δi) such that |x-a|<δi implies |f(x)-Li|<(L2-L1)/3

dawn zealot
#

How would I relate the epsilon to the delta?

opal pelican
#

In other words: there exists some interval radius δi, such that if x is in (a-δi,a+δi), then f(x) is in (Li-ε,Li+ε), where ε is (L2-L1) in our particular case

#

That is, your deltas are the radius of intervals that "force your function inside other intervals", for intervals as small as you'd like

dawn zealot
#

Okay

#

I still don't really know how to make the delta equal some epsilon

opal pelican
dawn zealot
#

Okay

#

What should I do instead?

opal pelican
#

We know that within some interval (a-δ1,a+δ1) something happens, and that within some other interval (a-δ2,a+δ2) something happens as well, they're both intervals centered on the same point, so you can verify that one will contain the other

#

Now, we want what happens in those intervals to happen at the same time, that is, the function to be within ε of both L1 and L2

dawn zealot
#

Okay. Thank you for your help! I have to go eat dinner now so sorry to not be able to finish this. Thank you for helping me start and understand this more

#

Have a nice day

#

.close

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burnt timber
#

on a function f(x) it's concave up if f''(x) is larger than 0 and cc down if f''(x) is smaller than 0 right? or is there more to this

burnt timber
#

and the inflection points are when f''(x) changes concavity?

junior token
#

if you ever forget which is which

burnt timber
#

alr thank you!

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next thorn
#

d/dx (sec(2x^2 + 2x))

sec(2x^2 + 2x)*tan(2x^2+2x)

and then, times the derivative of the angle itself... my question is, how many times?

next thorn
#

2x^2 + 2x is repeated twice

#

so do i multiply by 4x + 2 twice or once...

obtuse grail
#

what

glossy zephyr
#

If your question comes from the fact of using the derivative of 2x^2 + 2x twice, no

next thorn
glossy zephyr
#

chain rule states: $\dv x f(g(x)) = f'(g(x)) \cdot g'(x)$

soft zealotBOT
next thorn
glossy zephyr
#

Here g(x) is the whole 2x^2 + 2x

next thorn
#

mhm

#

so its repeated once

#

got it!

#

ty

#

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sacred night
#

Factorise $x^{12}-y^{12}$

final saddleBOT
sacred night
#

!status

final saddleBOT
#
What step are you on?
1. I don't know where to begin.
2. I have begun but got stuck midway.
3. I got an answer but I was told that it's wrong.
4. I got an answer and would like my work checked.
5. I have a question about someone else's work/solution.
6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
sacred night
#

1

soft zealotBOT
#

calvin

sacred night
#

is it $(x^6 + y^6)(x^6-y^6)$

soft zealotBOT
#

calvin

tribal crescent
sacred night
#

is it x^6 tho

#

idk if it is

tribal crescent
#

yeah

#

it is

sacred night
#

is tho

#

Is it tho

tribal crescent
#

(x^6+y^6)(x^3+y^3)(x^3-y^3)

#

shud be ur ans

sacred night
#

im confused tho

#

why cant we do x^6 + y^6

#

WIt but

#

Wait

#

X^6 wouldnt work

#

Would it?

#

Wair nvm

#

Im stupid

#

ty

#

.close

final saddleBOT
#
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tribal crescent
#

what are you asking bro

sacred night
#

I forgot my exponent laws for a second

candid pulsar
#

few more steps

#

use $x^3+y^3 = (x+y)(x^2-xy+y^2)$ and $x^3-y^3 = (x-y)(x^2+xy+y^2)$ to further simplify $x^6-y^6$ and $x^6+y^6$

sacred night
#

How

soft zealotBOT
candid pulsar
#

$x^6+y^6 = (x^2)^3 + (y^2)^3$

soft zealotBOT
candid pulsar
#

and $(x^2)^3 + (y^2)^3 = (x^2+y^2)((x^2)^2 - (x^2)(y^2) + (y^2)^2)$ according to that formula

soft zealotBOT
candid pulsar
#

im guessing you are asked to factorize to the maximum possible extent and not just once

final saddleBOT
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mint mural
#

How to know if you can factor something or not?

craggy plank
tired walrus
#

what class of "something"

#

polynomials? numbers?

craggy plank
#

what Ann said this

pliant shore
craggy plank
#

okay, I just checked your other thread

#

Looks like you’re trying to factorize polynomials

craggy plank
mint mural
#

For example can you factor

x^2 + x + 4

cosmic perch
#

$ax^2+bx+c = a(x-x_1)(x-x_2)$

soft zealotBOT
#

Labyrinth

cosmic perch
#

where x1 and x2 are the roots of x

#

This always works

#

However, I'm guessing you're restricted to real numbers, will have to check

pliant shore
#

I mean if you allow irrational and imaginary roots, any quadratic is factorisable

#

if you want only real roots, the condition is discriminant >= 0

#

if you want only rational roots, the condition is discriminant = perfect square

mint mural
#

I mean like this

pliant shore
#

oh, those

#

basically that's about if you can match it to the given form

#

say if you have 8z^3 - 125

that's (2z)^3 - 5^3, so you can use the form for a^3 - b^3

craggy plank
#

perfect squares and cubes

mint mural
#

Do the first one please

final tangle
#

wdym by do the first one

leaden moon
#

they sent this in another channel

leaden moon
soft zealotBOT
#

1 divided by 0 equals Infinity

leaden moon
#

if $\Delta \geq 0$, it's factorizable

soft zealotBOT
#

1 divided by 0 equals Infinity

leaden moon
#

else, you can't factor it

#

specifically, if $\Delta = 0$, you can turn your quadratic into a perfect square

soft zealotBOT
#

1 divided by 0 equals Infinity

leaden moon
#

@mint mural

mint mural
#

How to turn it into perfect Square boy?

#

<@&286206848099549185>

lunar jewel
#

Yes?

#

Looks like I have been summoned

#

@mint mural

mint mural
#

Do it

#

How to put it on x axis

lunar jewel
#

Do what?

#

Put what??

#

???

mint mural
#

I got 3 + sqrt(11) and 3 - sqrt(11)

lunar jewel
#

Please uhh ping taht exact equation

#

Like

lunar jewel
#

Heelloooo

#

@mint mural

mint mural
#

those are fucking zero points

lunar jewel
#

Huh

#

Wdym

#

Points?

final tangle
#

get their decimal approximation

#

put a scale on your graph

#

and put a point around that approximation

mint mural
#

Ok @final tangle

final saddleBOT
#

@mint mural Has your question been resolved?

leaden moon
#

!original

final saddleBOT
#

Please show the original problem, exactly as it was stated to you, with the entire original context. A picture or screenshot is best. If the original problem is not in English, then post it anyway! The additional context might still be helpful. Do your best to provide a translation.

leaden moon
#

because it seems like im confused of what you are trying to ask

#

firstly, you asked when is a polynomial factorizable, secondly, you go on with your zero points

#

what question are you trying to encounter?

mint mural
#

.close

final saddleBOT
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versed dawn
#

Hi, is my solution right? Probability item 🥲

Mia draws two pens one after another from a box that contains 5 red pens and 6 blue pens, without putting any pen back. Let X be the random variable that indicates how many blue pens she draws. Determine the possible values of X. Compute the mean of the probability distribution.

pliant shore
#

given there are 5 red pens and 6 blue pens, what's the probability Mia draws a red pen?

versed dawn
#

is it 5/11

pliant shore
#

alright, and we take the red pen out, so now there are 4 red pens and 6 blue pens

versed dawn
#

wait is the first or second table wrong

pliant shore
versed dawn
#

cuz what i did, i based it off the first table

pliant shore
#

once you get the logic for RR (X = 0) the rest will follow

versed dawn
#

but arent we looking for the blue pen tho

pliant shore
versed dawn
#

oh right

#

4/10?

pliant shore
versed dawn
#

then simplify

pliant shore
#

and now you can just multiply the probabilities

#

P(RR) = 5/11 * 4/10

pliant shore
versed dawn
#

Determine the possible values of X. Compute the mean of the probability distribution.

pliant shore
#

you've done 'determine the possible values of X' correctly

#

well you just needed to write X = {0, 1, 2} but your table is fine

versed dawn
#

how do i do the 2nd table tho, sorry i just based it off my teachers lesson

pliant shore
#

you need to find P(RR), P(RB), P(BR), P(BB) first

versed dawn
#

then separate tables for that in the format of 2nd table?

pliant shore
#

once you find the correct probabilities, then you can do 0 * ... + 1 * ... + 2 * ...

#

you can't just assume the probabilities are 1/4, 2/4, 1/4

versed dawn
#

okii, ill write them down first

pliant shore
versed dawn
#

Oh

#

Ok

pliant shore
#

otherwise, that's correct

versed dawn
#

Do i repeat the 1

pliant shore
versed dawn
#

Ohhh

versed dawn
#

It got a decimal

#

Uh

pliant shore
#

,calc (5/11 * 6/10 + 6/11 * 5/10) + 2 * 6/11 * 5/10

soft zealotBOT
#

Result:

1.0909090909091
pliant shore
#

there's nothing wrong with decimal answers

versed dawn
#

Oh yeah

pliant shore
#

we're just looking for our expected number of blue pens to be between 0 and 2

viral jungle
#

minor nitpick: is P(X) supposed to be a probability or an expected value?

pliant shore
#

it actually makes sense that our answer is near 1, actually

if we make it 5 red pens and 5 blue pens
and we do it with replacement

then that's just the setup of a fair coin

pliant shore
viral jungle
#

if it is meant to be an expected value, may I suggest using E(X) instead

#

ah

versed dawn
#

So 1.09 is the mean?

viral jungle
#

right, sorry to interrupt

pliant shore
versed dawn
#

No prob

pliant shore
#

wasn't looking carefully enough haha

versed dawn
#

I get it noww, tyzm for teaching my slow brainer 🥹

pliant shore
#

no worries!

versed dawn
pliant shore
#

it's not needed

versed dawn
#

okaayy

final saddleBOT
#

@versed dawn Has your question been resolved?

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pure cliff
final saddleBOT
viral jungle
#

have you tried sketching the problem?

pure cliff
#

no

#

ill do now

#

i have the line AB

#

but idk how i would sketch point C dividing

viral jungle
#

well, C has to lie on the line in order to divide AB, yes?

pure cliff
#

so ill just plot it at a random place

viral jungle
#

and given AB as a line segment and C dividing it in the ratio 1:3, which side do you think would be longer: AC, or BC?

pure cliff
#

Bc

viral jungle
#

absolutely

#

so make sure your diagram reflects that.

pure cliff
#

ok i have that

#

now what

viral jungle
#

where's the diagram?

pure cliff
#

wdym

#

you want me to send it?

viral jungle
#

well yeah

#

we can't work with it otherwise

pure cliff
#

im doing it on my ipad ill take a photo

viral jungle
#

right.
so, you are given that BC:AC = 3:1.

#

have you learnt about the distance formula?

pure cliff
#

ye

viral jungle
#

if you have, you can apply it here.
use the fact that the distance from C to B is 3 times that of A to C

#

let the coordinates of B be (x, y), then solve for that

#

or, to simplify, you can solve one component (x or y) at a time

#

which is easier and less headache to track

pure cliff
#

the distance formula is abs ax1+by1+c abs / sqrt a^2 + b^2

#

right

viral jungle
#

ack, might be overcomplicated here

rocky girder
#

you can use this formula where

B(x2,y2) A(x1,y1)

viral jungle
#

actually, just do it component-wise. I think it's easier that way

pure cliff
#

ik this one

rocky girder
#

it gives you a point in a ratio

viral jungle
#

yeah this works

rocky girder
#

try and use that one and see if that works

pure cliff
#

(21,5)

#

ye

#

its right

rocky girder
#

nice

pure cliff
#

thanks im prob gonna need more help in a few mins

final saddleBOT
#

@pure cliff Has your question been resolved?

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sharp wraith
#

find all functions that satisfy f(2x) = f(x) for all positive integers, how are you meant to approach this, i found that f(1) = f(2) = ... = f(2^k), and that f(3) = f(2^k 3), therefore f(2k+1) = f(2^k(2k+1))

tired walrus
#

that feels like either underspecified or a really wide class of functions hmmcatfone

lucid nymph
#

It would probably have to be either a constant or a sinusoidal function since it only means for all positive integers

sharp wraith
#

hmm ok

#

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supple nest
final saddleBOT
supple nest
#

Making sure my answer suffices

#

For how nasty a lot of proofs are this one seems pretty simple

shadow marlin
#

What is "a" for ?

final saddleBOT
#

@supple nest Has your question been resolved?

boreal lichen
#

dyadic folding identity

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distant scarab
#

,, \sum_{k=1}^\infty \frac{n^2}{n+k}

final saddleBOT
distant scarab
#

how to calculate this limit

soft zealotBOT
vital crag
#

looks like it diverges for most n

distant scarab
#

wait idk if what i wrote is correct

#

its $\lim_{n \to \infty} \sum_{k=1}^n \frac{n}{n^2+k}$

#

no way i wrote it inverted

soft zealotBOT
distant scarab
#

@rustic sequoia

atomic moon
#

Try to write it as a riemann sum

distant scarab
atomic moon
#

Never mind you can brutally make an asymptotical equivalent of the term inside

#

cancel n on top and bot

distant scarab
atomic moon
#

You agree this is the same as : n/n²(1+k/n²)

#

So this is 1/n(1+k/n²)

#

Look at k/n² for k in {0,...,n} and n tends to +inf

#

Think and tell me

distant scarab
floral nova
#

If you know enough complex analysis, the way I would approach it is to use the difference equation $$\psi(x+N+1)-\psi(x) = \sum_{k=0}^{N} \frac{1}{x+k}$$. You can then use the $\psi$ to telescope it down.

soft zealotBOT
#

JessicaK

distant scarab
#

i see it now , the limit is 1

atomic moon
distant scarab
#

it would just cancel out as n -> infinty

atomic moon
#

I was thinking of saying that 1/n(1+k/n²) ~ 1/n and so you sum on it and its just (n+1)/n which tends to 1 indeed

distant scarab
#

.close

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whole halo
#

Let G be a finite simple group. Let p be a prime dividing |G|. Let H ≤ G be the group generated by all elements of order p. Prove that G = H.

hasty mist
#

What have you tried?

whole halo
#

the only thing I can think of is that I need to prove that H is a normal subgroup of G, other than that Ive got nothing

whole halo
#

oh goddammit

#

I crossed that out because I didnt do it right

#

.close nevermind on this question too then

final saddleBOT
#
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whole halo
#

absolutely bombed the final exam because nothing I could think of seemed to work
I didnt even try and work with the ideas I had
thats 2 out of 3 questions I couldve finished had I stuck with them for longer

#

spent an entire half of the exam time staring at those 3 questions

final saddleBOT
#
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digital wave
#

If A is a group, is (A)^n also a group? What about (Z2)^n?

trail mango
#

what's (A)^n?

#

direct product?

digital wave
#

Group with the group set being Cartesian producted with itself n times

trail mango
#

okay

digital wave
#

The group operation becomes the original group operation of all individual elements from the sequence

trail mango
#

do you think it's a group?

digital wave
#

(a1, a2,...an)#(b1,...bn) = (a1b1, ..., anbn)

digital wave
#

Feels like it should be

trail mango
#

do you need to prove it?

digital wave
#

No, I just want to know if it's true in general or not

trail mango
#

oh

#

well yes

digital wave
#

Oh

trail mango
#

that operation is called direct product of groups

digital wave
#

Ohh

trail mango
#

usually you would write it like $$\prod_{i=1}^n A$$

soft zealotBOT
#

slayla

digital wave
#

I see

#

Very voolhappy

#

cool*

#

Thanks

#

.close

final saddleBOT
#
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trail mango
#

no problemo

digital wave
#

. reopen

#

.reopen

final saddleBOT
digital wave
#

So like

#

Does it fail for other structures

#

What about rings ornfields

#

It feels like I remember it failing somewhere

opal pelican
digital wave
opal pelican
#

One thing, though:

trail mango
#

ummm

#

no

opal pelican
#

In the case of a field, it not necessarily preserves field structure

#

But it will preserve the ring one

trail mango
#

RxR is not a field

digital wave
#

Ah yes.

#

It fails for fields

opal pelican
digital wave
#

Can I keep the channel open for further questions or make a new channel everytime

#

Bcz I will have more questions

trail mango
#

whatever you want. but you should probably close if you won't have any new questions soon

digital wave
#

blobcry okay

#

Bye

#

.close

final saddleBOT
#
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digital wave
#

I think it fails for integral domains too

trail mango
#

why do you cry all the time

digital wave
#

Sorry

trail mango
#

it's ok

scarlet sequoia
#

(a,0) * (0,b) = 0

digital wave
#

Yeah

final saddleBOT
#
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halcyon fog
#

Suppose tan theta=x and theta is in quadrant 2, such that x<0. Determine the exact values of sin theta, cos theta, sec theta, csc theta, and cot theta in terms of x. Review before my final and i got i got sin =-x/root x^2+-1^2 (abbreivated from now on as z). sec= z/-1. cos=-1/z. csc=z/x. cot= -1/x. I used an A.I to fact check and its just confusing me. Since its quadrant 2 x is negative so x/-1 as sin is positive in quadrant 2 and cosine is negative, the A.I is saying cot theta= 1/x but isnt it -1/x?

halcyon fog
#

nvm got it

#

.close

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final saddleBOT
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heavy sparrow
final saddleBOT
craggy plank
#

I don’t know the complete solution to the entire question, but can provide you some information regarding certain options

heavy sparrow
#

I tried jensen

#

But,I am confused when the double derivative sign changes in second quadrant

shy mantle
heavy sparrow
#

Jensen inequality

shy mantle
#

ooo

#

seems interesting

final saddleBOT
#

@heavy sparrow Has your question been resolved?

silver dew
#

You are on the right track

#

cos,sin,tan, one of them is concave finction

#

And (A+B+C)/3 is constantly π/3

#

One of them is concave on [0, π] I meant

silver dew
#

Interesting, Jensen leads you to one correct option, but actually two options are correct

chilly flume
#

Interesting , I forgot what's jensen

#

I did this in my jee time

silver dew
#

Google

#

Sum of cos = 1+(radius of inner circle/radius of outer circle) and the last term has a range (0,1/2].
you need to use this to deduce the another correct option. If this requires you to select only one, select the one Jensen leads you. The person gave you this exercise probably didn’t expect you to come up with two.

proven radish
final saddleBOT
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final saddleBOT
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spark swan
#

do we really need to use MVT?
can't we make |f_n(x)-f_n(x_0)| and |f_m(x)-f_m(x_0)| arbitrary small by uniform continuity, since each f_n is differentiable which implies continuity and [a,b] is compact so it's uniformly continuous
and |f_n(x_0)-f_m(x_0)| arbitrarily small because f_n converges at x_0
f'=g because of another already proved theorem (basically this theorem but f is assumed to converge pointwise)

final saddleBOT
#

@spark swan Has your question been resolved?

gloomy river
#

you can only make |f_n(x) - f_n(x_0)| small if x is close to x_0

silver dew
#

Then you shouldn’t consider it alone, but two , m and n together

#

$(f_{n}(x)-f_{m}(x))-(f_{n}(x_{0})-f_{m}(x_{0}))=\int_{x_{0}}^{x}(f_{n}’(t)-f_{m}’(t))dt$

#

Just as the hint said

soft zealotBOT
#

Cogwheels of the mind

silver dew
#

|x-x_0|<=b-a and the thing in the integral can be really small

gloomy river
#

is this about what I said?

spark swan
spark swan
silver dew
#

f_n’ converge uniformly, so f_n’ is Cauchy uniformly

spark swan
#

so i just set the integrand to be less than epsilon/(b-a)

#

thank you @silver dew and @gloomy river

#

.close

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#
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#
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distant scarab
#

,, \lim_{x \to 0} \left( \frac{2}{\sin(x)^2} - \frac{1}{1-\cos(x)} \right)

soft zealotBOT
distant scarab
#

how to evaluate this limit

#

wait i guess i'd gather the 2 expressions

frosty sigil
#

Simplify it into 1 eq first, it might help

#

Sin²x can be 1-cos²x

#

1-cos²x => (1+cosx)(1-cosx)

#

Then you should be able to make it into 1 eq then see how to go bout it starting from there

distant scarab
soft zealotBOT
distant scarab
#

,, \left( \frac{2}{\sin(x)^2} - \frac{1}{1-\cos(x)} \right) = \frac{1-2\cos(x) + \cos(x)^2}{(1-\cos(x)) \cdot \sin(x)^2} = \frac{((1-\cos(x))^2}{(1-\cos(x)) \cdot \sin(x)^2}

soft zealotBOT
distant scarab
#

what now ?

#

still get 0/0

frosty sigil
wraith tide
#

i am think it must be this

distant scarab
distant scarab
frosty sigil
wraith tide
distant scarab
frosty sigil
#

But it needs to be simplified further

distant scarab
#

can u elaborate

#

at the end the limit is : $\frac{1-\cos(x)}{\sin(x)^2}$

soft zealotBOT
coarse coral
wraith tide
distant scarab
#

its 1-cos(x) in the denominator

frosty sigil
# soft zealot

sin²x can be 1-cos²x which can be (1+cosx)(1-cosx) then the (1-cosx)s can be cancelled out

frosty sigil
coarse coral
frosty sigil
final saddleBOT
# coarse coral

The purpose of this server is to help you learn, not to hand out answers. Do not ask someone to give you the answer directly.

final saddleBOT
#
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#
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wraith tide
final saddleBOT
wraith tide
#

.close

final saddleBOT
#
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final saddleBOT
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distant scarab
#

$\lim_{x \to 0} \frac{e^{2x} +5e^x -6}{e^x-1}$

soft zealotBOT
distant scarab
#

i need a hint to solve this limit

#

hopital not allowed

loud sundial
#

factor

tired walrus
#

first and foremost

#

why not substitute y := e^x

#

it's practically begging to be made

#

$\lim_{y \to 1} \frac{y^2+5y-6}{y-1}$

soft zealotBOT
distant scarab
#

now its clear thx

#

.close

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#
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final saddleBOT
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tranquil pine
#

hiiii could i get some help on this pls

final saddleBOT
#
What step are you on?
1. I don't know where to begin.
2. I have begun but got stuck midway.
3. I got an answer but I was told that it's wrong.
4. I got an answer and would like my work checked.
5. I have a question about someone else's work/solution.
6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
tranquil pine
#

tbh idk where to begin

#

shoudl i attempt proof by induction

#

pls help me 😭

#

knief cmon 😭

rocky tusk
#

do you think it’s true?

tranquil pine
#

a

#

i mean it is right

rocky tusk
#

ok so what’s the issue

tranquil pine
#

how do i prove it

rocky tusk
#

did you use the definitions they gave above?

tranquil pine
#

ngl i didnt

tranquil pine