#help-36

1 messages · Page 109 of 1

chilly cloud
#

Let $f_n$ be cauchy in $L^\infty$. Then for for all $\epsilon>0$, there exists $N(\epsilon)$ natural such that for all $n,m>N$, $||f_n-f_m||_\infty<\epsilon$

soft zealotBOT
#

lilyenjoyer

chilly cloud
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Carve out the bad set $E_n,m$ where this doesnt hold, and take the union on n and m, countable so it just doesnt hold on some measure 0 set

soft zealotBOT
#

lilyenjoyer

chilly cloud
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now work on complement

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We have that ${f_n(x)}$ is cauchy (as a sequence of numbers)

soft zealotBOT
#

lilyenjoyer

mint orbit
chilly cloud
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now, let f(x) be the pointwise limit of f_n(x)

mint orbit
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I mean what does this do to epsilon

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we have no idea what the bound is anymore, do we?

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or do we not care

chilly cloud
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ok one thing at a time

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the inequality doesn't hold on $E_n,m$ but this has measure 0

soft zealotBOT
#

lilyenjoyer

chilly cloud
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then, $\cup_n \cup_m E_n,m$ is still a countable union, so it has measure 0 as well

soft zealotBOT
#

lilyenjoyer

chilly cloud
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where n,m are naturals

mint orbit
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no but i mean

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what are the variables we are using N n and m

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so for each epsilon, there is some N

chilly cloud
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This is from definition of cauchy

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yes

mint orbit
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I know

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but epsilon determines N

chilly cloud
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yes

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N(\epsilon) n depends on it

mint orbit
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and N determines what m and n are allowed

chilly cloud
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yes

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and now we take a hammer

mint orbit
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do these all have the same epsilon?

chilly cloud
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and eliminate the set

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where it doesnt hold

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for all possible m,n

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its measure 0, so it doesnt change anything

mint orbit
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im worried about the set where it does hold

chilly cloud
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ok wait

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do u see a problem with anything i type so far ?

mint orbit
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yes im asking about the bound

chilly cloud
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which one

mint orbit
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I don't understand how we can take a union and retain cauchy

chilly cloud
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i havent done anything yet outside of state cauchy

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Because the union is E_n,m

mint orbit
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the union should destroy the bound

chilly cloud
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is taken on a set of measure 0

mint orbit
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I guess i dont understand what these sets are

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I mean how one individual set is created

chilly cloud
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Forget that part for now

mint orbit
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We fix epsilon, N, m, n?

chilly cloud
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I come back

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to that part

mint orbit
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its a big part lol

chilly cloud
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yes

mint orbit
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I don't get what you mean we destroy the place where bad things happen

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I mean this union doesnt seem to accomplish that

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it creates more problems

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because now we cant talk about cauchy

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but maybe we can and i just dont understand what the union is working on

chilly cloud
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do you know what infinity norm is?

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can you say how it is defined

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for yo

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you*

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L^infinity norm

mint orbit
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ugh maybe i should scribble

mint orbit
chilly cloud
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norm like

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Does it look like this?

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The way you have it

mint orbit
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right

chilly cloud
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yes

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ok the important part here is

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a.e. x

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we ignore all sets of measure 0

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right?

mint orbit
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so when we say $||f_n -f_m|| > |f_n-f_m|$ this is fixed m n?

soft zealotBOT
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jan Niku

chilly cloud
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yes if we qualify it that way

mint orbit
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and then you say EXCEPT

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on the set Zmn

chilly cloud
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yes

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but Z_mn is measure 0

mint orbit
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so if you U {mn} Z{mn}

chilly cloud
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sure

mint orbit
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you get say Z

chilly cloud
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we agree that this union is also measure 0?

mint orbit
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yea

chilly cloud
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and that for all m,n

mint orbit
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so now you have Z

chilly cloud
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outside of Z, the inequality holds

mint orbit
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so if you exclude Z

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then it doesnt matter really what m,n are

chilly cloud
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exactly

mint orbit
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because Z_mn is in there

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okay

chilly cloud
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thats the point

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we want to work with infinitely many m,n later

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so carving out Z is important

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Can i move on

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to the uniform convergence now?

mint orbit
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sure, sorry

chilly cloud
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its ok

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its fun lol

mint orbit
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this is the part that i was most confused on 😓

chilly cloud
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i havent seen this in a while

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oh

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you get everything else?

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or no

mint orbit
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but i dont understand the rest either KEK

chilly cloud
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o

mint orbit
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but this is what made me give up

chilly cloud
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ok sure

mint orbit
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and go home and eat burritos

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for 1 hour

chilly cloud
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SO now we're back to

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f_n being cauchy

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now, we fix x inside $Z^c$

soft zealotBOT
#

lilyenjoyer

mint orbit
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sure

chilly cloud
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we have that $f_n(x)$ is a cauchy sequence

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of real numbers

soft zealotBOT
#

lilyenjoyer

chilly cloud
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now, define $f(x)=lim_n f_n(x)$

soft zealotBOT
#

lilyenjoyer

mint orbit
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we dont know this exists

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do we

chilly cloud
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yes

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reals are complete

mint orbit
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cauchy isnt enough for convergence

chilly cloud
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this is a sequence of real numbers

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we fixed an x

mint orbit
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its a cauchy sequence

chilly cloud
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yes

mint orbit
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but we dont know it converges

chilly cloud
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cauchy implies complete

mint orbit
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it may just be cauchy

chilly cloud
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sorry

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thats dumb typo

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cauchy implies convergent

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when you have a sequence of reals because R with standard metric is complete

mint orbit
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I'd have to check this is true

chilly cloud
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and this is a pointwise limit

chilly cloud
mint orbit
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cauchy implies convergent

chilly cloud
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ok wait

mint orbit
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it doesnt seem like itd be true

chilly cloud
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do we agree that

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for sequences of real numbers

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if a_n is cauchy, it is convergent?

mint orbit
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I don't recall this as a fact it doesnt seem like itd be true

chilly cloud
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wait

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what

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this might help u

mint orbit
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i mean it seems like okay log(n) would be one-

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cauchy but not convergent

chilly cloud
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no no

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forget all functions

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rn

mint orbit
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but this is a counter example

chilly cloud
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take a sequence of real numbers cuachy

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there cannot be a counter example

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to the reals being complete

mint orbit
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log(n) is a sequence of real numbers

chilly cloud
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its not cauchy

mint orbit
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n=1,2,3,...

chilly cloud
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log(n) is not cauchy

mint orbit
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thonk maybe i messed up my proof

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i was arguing with someone about this earlier irl

chilly cloud
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😭

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i think

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the most easy way to see this

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is the cauchy construction fwiw

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not the dedekind one, it hurts my brain

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but its also in rudin i think, ch1 or appendix i forgot

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but if you can accept that the reals are complete i can finish the proof of L^ infty complete

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err just ping me if u want me to continue

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illstill be on doing hw

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😂

mint orbit
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i need to check on what you are talking about

chilly cloud
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sure sure

mint orbit
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i dont believe it is true so i want to believe

chilly cloud
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😭

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ok wait

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i can ask in the real complex channel LOL

mint orbit
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im sure youre right

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i dont belong in this class i dont know any analysis

chilly cloud
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its ok lol

mint orbit
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im just trying to do my best

chilly cloud
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i dont mind im not an analyst no money in math

chilly cloud
mint orbit
chilly cloud
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its ok!

#

In mathematical analysis, a metric space M is called complete (or a Cauchy space) if every Cauchy sequence of points in M has a limit that is also in M.
Intuitively, a space is complete if there are no "points missing" from it (inside or at the boundary). For instance, the set of rational numbers is not complete, because e.g. 2{\displaystyle {\s...

mint orbit
#

always know im really reviewing some shit i shouldnt have forgot when author starts asserting stuff like 1>0

mint orbit
#

sorry im proving cauchy implies convergent

chilly cloud
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well this is not true unless ur space is complete

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but then its definition

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the theorem is proving R is complete by construction

mint orbit
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im not even sure what complete means tbh

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but each thing in turn

chilly cloud
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X is complete <=> (x_n cauchy => x_n converges)

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for x_n sequence in X

chilly cloud
mint orbit
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I'm trying to prove it for the reals

chilly cloud
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oh ok

mint orbit
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im stuck on a lemma

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sorry

chilly cloud
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its ok lol

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ill be up for a while anyways doing hw

chilly cloud
mint orbit
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i dont get the last line blobsweat

chilly cloud
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it gets hairy

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are you looking at the construction of R

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from equivalence classes?

mint orbit
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no im looking at a proof that cauchy implies convergent opencry

chilly cloud
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that divides in half nonstop

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have fun lol

mint orbit
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no im trying to follow this

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im not doing anything cool sadcat

chilly cloud
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oh

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the proof i mentioned was of

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bolzano weierstrass

mint orbit
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no i cannot prove everything i dont understand

chilly cloud
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ok yea lol mb

mint orbit
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some stuff you just have to take at face value

chilly cloud
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which line r u stuck on

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yea

mint orbit
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the second to last line

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it looks like triangle ineq

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but its not

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|am - an| should be |am -ans -an + ans|?

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but they inttroduce ell somehow

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and remove a_n?

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idk im probably like

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i dont know enough analysis to complete this problem bearlain

mint orbit
#

is that the end of the proof you were talking about

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i forgot where we even were now

chilly cloud
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of which

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uniform conv

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uniform convergence?

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yes it's nearing the end

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if you take for granted that the reals are complete, you have it almost immediately

mint orbit
#

so we defined okay

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we defined Z as the problem set

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so on Z^c, if you fix some x in Z^c

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then

chilly cloud
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f_n(x) is cauchy, but these are just real numbers

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so define f(x) = lim f_n(x)

mint orbit
#

then |fm - fn| < ||f_n - f_m||?

chilly cloud
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uhhh

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which metric do you have here?

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the one induced by L_infty norm?

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but i was gonna say

mint orbit
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its that if x is in $Z^c$ that $||f_n - f_m|| > |f_m - f_n|$ for all $m,n > N$

soft zealotBOT
#

jan Niku

chilly cloud
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we have that yes

mint orbit
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okay

chilly cloud
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then, we have an f

mint orbit
#

and this means that f_n is cauchy?

chilly cloud
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yes

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from that inequality

mint orbit
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how do we know blobsweat

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oh i guess we assumed it was true

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we dont have to show it

chilly cloud
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Let e>0, choose n_0 such that ||f_m-f_n||<\e for all m,n>n_0

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then we have the inequality so it is cauchy

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then we define f(x) as the pointwise limit

mint orbit
#

what do you mean by inequality

mint orbit
chilly cloud
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$|f_m(x)-f_n(x)|\leq ||f_m-f_n||_{\sup} <\epsilon$

mint orbit
#

did we have to do extra work for f_n to be cauchy

chilly cloud
#

no

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its basically a given

mint orbit
#

but we had to do work to ensure it was true for this fixed x

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okay

soft zealotBOT
#

lilyenjoyer

chilly cloud
#

have you seen that

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pointwise limit is measurable

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then f is measurable

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since $f(x):=\lim_n f_n(x)$

soft zealotBOT
#

lilyenjoyer

chilly cloud
#

and we have that f(x) exists for all x since each f_n(x) is cauchy

chilly cloud
mint orbit
chilly cloud
#

o ok

mint orbit
#

but f is already measurable

chilly cloud
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huh

mint orbit
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or i guess this is just called f who the hell knows if thats what it means

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im not sure why thats there

chilly cloud
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we constructed such an f

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but yes its measurable

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its different from the f there

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but tldr its nice either way

mint orbit
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do we care how we know fn is measurable

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or they just have to be

chilly cloud
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f_n is in L^p

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so its already measurable

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by definition

mint orbit
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but we havent shown completeness yet so we dont know that the pointwise limit is measurable

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okay

chilly cloud
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pointwise limit of measurables is measurables fwiw

mint orbit
#

im sure its true

chilly cloud
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but to continue

mint orbit
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okay so its convergent

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and its measurable

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so all thats left to show is that its essentially bounded

chilly cloud
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yes so now take limit

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from earlier: Let $\epsilon>0$, choose N so that when $n,m\geq N$, this holds $|f_m(x)-f_n(x)|\leq \epsilon$

soft zealotBOT
#

lilyenjoyer

chilly cloud
#

then as $n\to\infty$ you have $|f_m(x)-f(x)|\leq \epsilon$

soft zealotBOT
#

lilyenjoyer

mint orbit
#

hmmm

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im not sure i follow

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i may stop for tonight

chilly cloud
#

sadcatthumbsup sorry im bad at explaining im just looking at my old lecture notes

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but after this theres 1 line and ur done

mint orbit
#

its not your fault i just dont understand anything in analysis

chilly cloud
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well, 2

mint orbit
#

we know its true for all n but why wont something else happen in the limit

chilly cloud
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by construction ig

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sorry thats not satisfying idk

mint orbit
#

i guess i will stop

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or maybe im curious

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@chilly cloud whats the last 2 lines

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u dont have to tell me blobsweat im not just gonna steal the answer

chilly cloud
#

its ok its fast lmao

mint orbit
#

in fact im gonna start over from the beginning as soon as you go to bed happy

chilly cloud
#

wel we have that

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f_m converges to f in L^infty norm

mint orbit
#

?

chilly cloud
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then triangle inequality

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oh cause after we take

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n to infinity

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we have that for $m\geq N$, $||f_m(x)-f(x)||_{\infty}\leq epsilon$

soft zealotBOT
#

lilyenjoyer

chilly cloud
#

but we have it true for all x in Z^c

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so now we pass back to sup (infty norm) that way

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and this is the L^infty norm so by definition we have that f_m goes to f in L^infty norm

mint orbit
chilly cloud
#

yea its convergence in norm

mint orbit
#

but this isnt everything

chilly cloud
#

yea theres a short step after

mint orbit
#

we didnt show f is essentially bounded

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also didnt we already show that the cauchy sequence was convergent to f

chilly cloud
#

yea its the last step

mint orbit
chilly cloud
#

we have this from

mint orbit
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whyd we do all this extra stuff

chilly cloud
#

its to get that our f

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is in L^infty

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i.e. essentially bounded

mint orbit
#

but it doesnt show that thonk

chilly cloud
#

the last step being triangle inequality

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$||f||\infty \leq ||f-f_m|| + ||f_m||\infty + \epsilon < \infty$

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$1$

soft zealotBOT
#

lilyenjoyer

chilly cloud
#

test

mint orbit
#

you have a space after your final symbol

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between $

soft zealotBOT
#

lilyenjoyer

mint orbit
#

i think i get it

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nm(f) <= nm(f-fm) + nm(fm) < eps + nm(f_m)

chilly cloud
#

ugh typos

mint orbit
#

but fm is essentially bounded

chilly cloud
#

sorry im on old laptop

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yes

mint orbit
#

so f is essentially bounded

chilly cloud
#

yes

mint orbit
#

at least i understand the last step happy

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maybe i will work backwards then

chilly cloud
#

the earlier step is the 'hard' one ig

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where you pass to the reals

mint orbit
#

i still do not understand tbh

chilly cloud
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to show that f(x) indeed does exist

mint orbit
#

i dont understand how we can use the reals here

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but office hours tomorrow

chilly cloud
#

ask ur prof to explain how

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the L^p completedness

mint orbit
#

i already know what she will say

chilly cloud
#

depends on the completedness of reals

mint orbit
#

she will say

chilly cloud
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its key ingredient

mint orbit
#

you should review your analysis

chilly cloud
mint orbit
#

lol

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sorry to keep you up mirin

chilly cloud
#

its ok

mint orbit
#

but

chilly cloud
#

my class not til 2

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only midnight

mint orbit
#

u know theres a helpers vc

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if u become helpful

chilly cloud
#

oh

mint orbit
#

we could pomo flonshed

chilly cloud
#

i only helped cuz i saw ur name

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😭

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sry

mint orbit
#

im in my last month of school lol

chilly cloud
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i dont help normally lmao

mint orbit
#

ah

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well

chilly cloud
#

oh me too

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dang

mint orbit
#

thats okay happy

chilly cloud
mint orbit
#

we will always have the memories

chilly cloud
#

last 2 months for me but

mint orbit
chilly cloud
#

onto the real world ig 😔

pliant shore
mint orbit
#

each day it looks bleaker

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but day at a time

chilly cloud
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job hunt catcros

mint orbit
#

yea that too

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i mean

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i have essentially no time

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but thats okay

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good luck on your finals if i dont see u mirin

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💪

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.close

final saddleBOT
#
Channel closed

Closed by @mint orbit

Use .reopen if this was a mistake.

mint orbit
#

@chilly cloud and thank you again happy

paper timber
#

hi guys

mint orbit
#

the channel will suddenly lock soon

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just so you know

paper timber
#

I was wondering, i Send pics of problems in the chat maybe someone could give me the answers?

paper timber
mint orbit
#

get an open channel

paper timber
#

Ok, thank you

final saddleBOT
#
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neat flint
#

someone mind checking my work?

final saddleBOT
neat flint
#

or would it be better to put -0.5

marsh temple
#

Your answer is fine, whether decimal is better depends on the software

final saddleBOT
#

@neat flint Has your question been resolved?

#
Channel closed

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Use .reopen if this was a mistake.

#
Available help channel!

Send your question here to claim the channel.

Remember:
Ask your math question in a clear, concise manner.
Show your work, and if possible, explain where you are stuck.
After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!

Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.

normal juniper
#

can someone please help me with this

final saddleBOT
muted wraith
#

so you have 1/root2 + i/root2 on rhs

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convert that to cis form

normal juniper
#

alr

normal juniper
muted wraith
#

yep

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the general form is cis(2pi(k)+ pi/4)

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then apply nth root on both sides

normal juniper
#

if it was roots of unity I get the 2pi(k)

muted wraith
#

pi/4, 2pi+pi/4,... all give the same value

normal juniper
#

oh ok

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oh yeah that makes sense

normal juniper
muted wraith
#

noo

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try again

normal juniper
#

wait what

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oh shit

normal juniper
#

coz then the modulus will be root 2

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but from the original thing it is 1/root2 + i/root2

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so when it multiplies it's going to become 1 + i

muted wraith
#

(cistheta)^1/n is cis(theta/n)

normal juniper
#

ooooohhh

normal juniper
muted wraith
#

yeah

normal juniper
#

ok that makes sense

#

thakns for the help

#

.close

final saddleBOT
#
Channel closed

Closed by @normal juniper

Use .reopen if this was a mistake.

final saddleBOT
#
Available help channel!

Send your question here to claim the channel.

Remember:
Ask your math question in a clear, concise manner.
Show your work, and if possible, explain where you are stuck.
After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!

Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.

neon slate
#

these definitions are from different books and one is about Rn and the other about complex numbers, but seems like either one could be used for the other set.

I was just wondering, would every accumulation point by these definitions also be a limit point and vice versa? My brain is new to thinking about sequences of points so not sure if i have the right intuition on this but seems like if you have an accumulation point you could pick successively smaller balls around it and picking points out of them to come up with a sequence of points that converges to that point. and i think also that if you have a limit point, you would need an infinite number of points in every ball around it since for at any point in the sequence, you would have an infinite number of upcoming elements within any desired radius of the limit point.

trail mango
#

yes

neon slate
#

😄

#

oops pinged wrong person lol

trail mango
#

nice ping

neon slate
#

so theyre equivalent?

trail mango
#

yes and your explanation is right

neon slate
#

i find the definition of accumulation points way more intuitive

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what would be motivation to think of limit points in terms of sequences?

trail mango
#

not sure. sequences are nice to work with tho

neon slate
#

or wait, in definition of limit point, do all the points need to be distinct?

trail mango
#

no

neon slate
#

someone on stack exchange was saying this

neon slate
#

oh hm

#

i guess theyre using a diff definition

trail mango
#

{1} doesn’t have any limit points or accumulation points with your definitions

neon slate
#

right

neon slate
# trail mango no

but you would need to end up with an infinite number of distinct points in the sequence right

#

cause otherwise if there were only a finite number, you could figure out the closest point's distance from the supposed limit point and there'd be no more points in the sequence if you pick epsilon < that i guess?

trail mango
#

yea

neon slate
#

so when youre building these sequences of points, youre basically stringing points one after another in whatever random fashion you want, the sequence of points converges if for any epsilon > 0 you can find some N so that after N all the points in the sequence afterward are within < epsilon distance from L right?

trail mango
#

you could say if z is a limit point of S then there is a sequence in S converging to z with all elements distinct and not equal to z

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but there will also be sequences that don’t have all elements distinct

neon slate
#

yeah i think that makes sense, cause you could just eliminate duplicates from whatever existing sequence i guess?

trail mango
#

yea

neon slate
#

oh uh

#

i dunno if thats the right word, just imagining these sequences, and basically was just having a bit of trouble with what a sequence of points even is, but i guess just literally any list of points lol

#

that goes on forever

#

and convergent ones i guess are special cause they become bounded by their distance to something?

#

but it could literally just be random points forever right? 😄

trail mango
#

yea. a way to look at what a sequence (in S) is, is that it’s a function from the positive integers to S

neon slate
#

righto

#

btw layla

#

today i fell asleep at 8pm

#

and woke up at 2 lol

#

guess i was just tired

trail mango
#

WTF

neon slate
#

.close

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trail mango
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past bronze
final saddleBOT
past bronze
#

can sshouldnt it be D

zealous reef
past bronze
#

its decreasing then increasing

#

so point of inflectio

#

i learned is f'(x) is under the x axis, then f(x) was decreasing

zealous reef
#

how would you define point of inflection

past bronze
#

concave up to concave down

#

or from negative to positive

zealous reef
#

concave up to concave down or vice verse doesnt mean the slope goes from negative to positive

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tired snow
#

Help?

final saddleBOT
final saddleBOT
#

@tired snow Has your question been resolved?

static plinth
# tired snow

so since the rod is in equilibrium, we can choose our pivot point anywhere to make it more convenient

#

i would suggest putting the pivot point on point A, so the normal force at point A would be canceled out

#

actually your last line is very close to the correct answer

#

double check the lever arm you’re multiplying by for R_p

final saddleBOT
#

@tired snow Has your question been resolved?

tired snow
#

I dont know the distance A-P

static plinth
#

we can use trig for that

tired snow
#

Wait

static plinth
#

also be careful that it is 45cm not 45m

tired snow
#

Ou thanks

#

This?

static plinth
#

yep

#

but we want the hypotenuse here

tired snow
#

Yeah

static plinth
#

actually you kinda labeled the adjacent side wrong as well

tired snow
#

Why

static plinth
#

you can only do that when the hypotenuse is given

tired snow
#

Oh

static plinth
#

since cos(15)=A/H

#

but we don’t know H

#

we only know O

tired snow
#

I need 2 sides

static plinth
#

so we have to relate sine with the opposite and hypotenuse

#

and solve for the hypotenuse

tired snow
#

How do I do that

static plinth
#

$\sin(15)=\frac{.45m}{h}$

soft zealotBOT
tired snow
#

Only 1 side is given

static plinth
#

how do we solve for h

tired snow
#

Oh that

#

I thought something else

static plinth
#

oh

#

were you going to use tangent?

#

to find the adjacent

#

and then use pythagorean to solve for hypotenuse?

tired snow
#

Messed up my bad

static plinth
#

alright all good

tired snow
#

Yeah its 25 now (shown)

#

As for part b if we do upward forces equal downward forces?

static plinth
#

we can

#

as long as you make sure to split up R_p into components

#

or we can use torque again

#

and place our pivot point elsewhere

final saddleBOT
#

@tired snow Has your question been resolved?

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rigid plinth
#

Is there supposed to be 2 sets of answers to this q? The answer key says its only r=8, theta=1/4

languid yoke
#

Well r=1 and theta=16 doesn't really make sense

#

since if r=1 the area of the full circle is pi which is less than 8

#

Also keep in mind that theta won't be higher than 2pi.

rigid plinth
#

Thanks

#

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wispy trellis
#

What is name of this formula/property??

final saddleBOT
vapid basalt
#

the proof is pretty simple

wispy trellis
#

Same like this what is for tan cot sec and cosec?

vapid basalt
#

unrelated to this one

wispy trellis
#

Okay thanks

#

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heavy grove
#

I determined a is 1 but that’s it

final saddleBOT
heavy grove
#

I tried solving for the horizontal asymptote of came up empty handed

vapid basalt
#

for c you have 2 possibilities

heavy grove
#

Yep

vapid basalt
#

either the function is undefined at that point or you have a global extremum at -1

heavy grove
#

I tried lhopital because I think it can apply here?? I got 1/2bx+c and so 2bx + c = 1 and if they can only be 1 and 0, c must be 1, and b must be 0.

#

Is that right?

vapid basalt
#

i had the wrong idea lmao

#

my bad

#

i need to sketch it gimme a sec

heavy grove
#

I think I need to solve for the horizontal asymptote and compare it?

#

But when I solve it normally it’s 0

#

Ignore x->0 that’s supposed to be inf

vapid basalt
#

i have a better idea

#

first reasoning for why a=0

heavy grove
#

Why would a be 0?

#

It’s 1

vapid basalt
#

i meant b sorry

neon slate
heavy grove
#

0 and 1

neon slate
#

so 1/(2b+c) = 1
well b is either 1 or 0, but if b is 1 then this fraction is < 1 so b = 0

heavy grove
#

Right

#

And c must be 1

neon slate
#

wait no 😄

vapid basalt
#

if b =1 it would have a vertical asymptote

neon slate
#

its 1/ (2bx+c) i guess

heavy grove
#

But what about when I take it normally

neon slate
#

so that limit would be 0 as x -> inf if x isn't 0

heavy grove
#

By dividing by x^2

#

I get 0

#

Why don’t I get 1?

neon slate
#

take what normally?

heavy grove
#

The horizontal asymptote

#

Solving for it normally it’s 0

neon slate
#

what does "take the asymptote normally" mean?

heavy grove
#

A different method of

neon slate
#

i am not understanding what youre trying to say

heavy grove
#

Ig

heavy grove
neon slate
#

so x-> inf?

heavy grove
#

Yes

#

The top becomes 0

#

And I can’t make it 1

neon slate
#

what do you mean becomes 0

#

as x-> inf, top -> inf

heavy grove
#

It approaches 0

heavy grove
#

That’s the way I was taught

neon slate
#

wut

heavy grove
#

Wdym

vapid basalt
#

@heavy grove you sure you took the limit correctly?

neon slate
#

so youre back where you started

heavy grove
#

0/b

neon slate
#

and how do you know b isn't 0?

#

as it turns out thats the case

heavy grove
#

Mmm

#

That’s a good point

#

So is lhopital the proper method here

neon slate
#

yea

vapid basalt
heavy grove
#

Is that probably what the wanted

vapid basalt
heavy grove
#

What other method was there

vapid basalt
#

no this is the method but i assume they want you to show that you know why it works

#

ie you approach a point with the slope 0

final saddleBOT
#

@heavy grove Has your question been resolved?

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fierce osprey
final saddleBOT
#

@fierce osprey Has your question been resolved?

final saddleBOT
#

@fierce osprey Has your question been resolved?

final saddleBOT
#

@fierce osprey Has your question been resolved?

muted wolf
#

u already found out the radius and height for the minimum cost, u just need to substitute the radius and height in the expression of their respective areas and find out the area and multiply with the cost of the material corresponding to the area, tada u found out the minimum cost

fierce osprey
#

how do I do the minimum accuracy

fierce osprey
#

thx

muted wolf
fierce osprey
#

!close

muted wolf
#

.close

#

ig

fierce osprey
#

.close

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magic loom
#

i have a theory question

final saddleBOT
magic loom
#

this is sin(x) with domain [0, 2pi]

#

if you calculate the area from 0 to pi it's 2

#

but the area from pi to 2pi is -2

#

but that doesn't rlly make sense does it

#

cuz it's an area

formal trail
#

integrals don't give the area, they give a "signed area", which says that area above the x-axis is positive and area below the x-axis is negative

magic loom
#

if my goal is to calculate the area then should i just put a negative before the integral sign

#

like this

#

O(W) just means surface

formal trail
#

if you have a function that is negative for an entire interval, then putting a negative in front will give a positive area

magic loom
#

yeah

#

so i think in this case adding the negative would give the correct area

#

since from pi to 2pi it's completely under the x-axis

jolly tapir
#

well just enclose it in absolute value then

magic loom
#

my book isn't a fan of that so i asked about the adding negative thing instead

jolly tapir
#

taking the absolute value works for all f(x) when you want to take the absolute area

#

as opposed to - which only works for this instance

magic loom
#

idk why they won't do that in the book

#

maybe it'll come later

#

i'll keep it in mind

#

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formal trail
# magic loom idk why they won't do that in the book

when we do absolute value, it's not practical to integrate. so we use the definition of absolute value [ \abs{f(x)} = \begin{cases} +f(x), & f(x) \ge 0 \ -f(x), & f(x) \le 0 \end{cases} ] which comes out to the same approach

soft zealotBOT
#

𝕔loud

magic loom
#

thanks a lot

final saddleBOT
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normal juniper
#

can someone please help me with this question

normal juniper
#

I'm pretty sure it involves using modulo but i'm not sure how

hollow iron
#

Try squaring both sides

normal juniper
hollow iron
#

No

normal juniper
#

wat

hollow iron
#

Try again and do it carefully

normal juniper
#

ohh crap

#

x^2 + 2 + 1/x^2 = 1

hollow iron
#

Yup

#

So what does x^2 + 1/x^2 equal to?

normal juniper
#

-1

languid whale
hollow iron
#

No don't do that

#

Alright so x^2 + 1/x^2 = -1

#

Try squaring both sides again..

#

You might notice something

normal juniper
#

ok so I assume it always equals to -1

hollow iron
#

Well not always, but for some powers it does

#

Specifically, powers of 2

normal juniper
#

right

#

so I find the power of 2 thats closest to 2016

#

?

#

1024 is the closest power

brave shoal
#

2048 is closer, is it not?

hollow iron
#

Yes it is

normal juniper
#

oh thats true

#

i thought it couldnt be above

#

so what now 🤔

hollow iron
#

Hmm

#

Actually x is just a third root of unity is it not

normal juniper
#

wait why

hollow iron
#

x + 1/x = -1
x^2 + x + 1 = 0

normal juniper
#

where'd the 1/x^2 go

hollow iron
#

What do you mean

#

Forgot the squaring thing, there's a simpler way

#

x^2 + x + 1 = 0 implies x^3 = 1

normal juniper
hollow iron
#

You can multiply both sides by (x - 1)

#

Yeah forget that

normal juniper
#

alr

hollow iron
#

So x^3 = 1 and you can easily use that to find the value of the expression you want

neon slate
normal juniper
hollow iron
#

The solutions to x^2 + x + 1 = 0 are two of the three solutions to x^3 - 1 = 0

#

The only one missing is x = 1

normal juniper
#

ah ok

neon slate
#

...no kidding you're introducing that solution by multiplying by (x-1) on both sides, but what does that have to do with the problem at all?

hollow iron
#

Because x^2016 = (x^3)^(672)

normal juniper
#

so the answer is a?

#

oh wait its 2

#

so b

hollow iron
#

Yes

normal juniper
#

oh ok

#

I just did the multiply both sides by (x-1) on paper and it makes sense

#

Thanks for the help

#

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undone idol
#

help

final saddleBOT
undone idol
lucid marsh
#

pi/2 +(pi/4-pi/6)

#

If i understand the question correctly

undone idol
#

why is this?

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faint condor
#

Could I get some hints on how to approach this, I’ve got the two equations by themselves in vector form but don’t know how to go any further

terse siren
#

try to write the equation of the line in terms of xyz

faint condor
#

Just a hint please

tiny gorge
#

your line equations have three rows
one for each of x, y and z

terse siren
#

yes

#

x = -3 + 7 * lambda for example

faint condor
#

Okay, thank you

terse siren
#

now i'd try writing the equation as x + ay + bz = 0

#

making it independent from lambda

faint condor
#

Got it @terse siren thanks for your help

#

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terse siren
#

np

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tame thicket
#

Can someone help me with this contest challenge?

tame thicket
#

I have finished this problem and I got it wrong. Can someone tell why?

#

I think the error can not come from the solving equations part because I have double checked

#

Probably the problem is in establishing the equations

zenith pollen
#

yea the equations get solved correctly, and I think the 5 degrees might be 30 degrees instead, if you mean the angle between numbers on a clock

tame thicket
#

Oh yes, the hour hand moves 360/12 = 30 each hour

#

Now the new system is
270 + x/2 = 6x + 360t - 360
6x = 270 + x/2 + 30t
solving I got t = 12/13

#

yes this is indeed the correct answer

#

thank you for help

#

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hoary oxide
#

yo

final saddleBOT
hoary oxide
#

I thought in symbolic logic, "AND" has precedence over "Implications"

lucid marsh
hoary oxide
#

so shouldn't the AND execute first (thus implicity parantheses over the Fat and Happy), and then the conditional?

lucid marsh
#

To emphasize why this is wrong

hoary oxide
#

thank u hired

#

< 3

#

.closed

#

wut

#

.close

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magic sparrow
#

@hoary oxide hello

hoary oxide
#

HEYYYY

hoary oxide
magic sparrow
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rugged tide
#

i'm at a loss here

final saddleBOT
static fractal
#

are you asking how the integral on line 2 evaluates to that?

rugged tide
#

no I drew an arrow with ??? on what i'mc onfused on

#

like what next

iron dagger
#

you isolate y

#

what is the inverse of the e function?

static fractal
#

move the minus to the other side and take logs

lucid marsh
#

Negate both sides and take the ln

rugged tide
#

ik isolate y but how do I do the thing to do that

tawdry storm
#

logs are the "opposite" of exponents

#

ln is base e

rugged tide
tawdry storm
#

Just remember, what you do to one side, you have to do to the other

iron dagger
#

more specifically the inverse of e, meaning that taking ln(e^x) = x

rugged tide
#

oh

#

Thanks all

#

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vital spruce
#

just wanted to verify since not much solved examples online, if i want to solve the tsp, can i define first two points as farthest point from middle as first point and closest point to that as second one?

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mortal horizon
#

Can someone check my logic? I think it’s 21, since for the number of distinct digits in this type of palindrome there are 2 options, so 2^n, but we have to subtract 2 since it can’t be all 8 or all 9. 2^11 - 2 = 2046, and 21 is the smallest length palindrome with 11 distinct digits

zenith pollen
#

that's right

mortal horizon
#

Ty

#

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wanton spindle
#

Stuck on part 1, I can do part 2 by reduction of order but I need an existing solution which I am having trouble coming up with from part 1

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@wanton spindle Has your question been resolved?

wanton spindle
#

<@&286206848099549185>

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restive copper
final saddleBOT
#

Please don't occupy multiple help channels.

sinful fox
#

a+b = 15

#

a-b= 4

#

a(radius of larger circle) b(radius of smaller circle)

#

than find the both radius

#

calculate their areas and substract them from rectangles area

restive copper
sinful fox
#

yes

restive copper
#

I worked it now however I got confused cause since there's no - on neither 15 or 4 it become 19

pliant shore
#

Do you see how that happened?

restive copper
#

ok i gotta sleep

pliant shore
#

Cool ok have a nice night

restive copper
#

im missing so many obvious steps bruh

sinful fox
restive copper
#

but yeah i understand it now

final saddleBOT
#

@restive copper Has your question been resolved?

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slim saddle
#

how many ways are there of choosing 3 different numbers in increasing order from the numbers 1,2,3,4,...,10 so that no two of the numbers are consecutive?

trail mango
#

there might be a better way but i have a stupid suggestion which is to count the number of choices that don't include 10 first

#

and to translate it to a combinatorics problem: I THINK choices that don't include 10 correspond to ways to place down two-length "blocks" onto the list 1,2,3,...,10

vital surge
#

this q is stars and bars problem so

trail mango
#

well it already is a combinatorics problem

slim saddle
#

what r two-length blocks?

trail mango
#

this corresponds to the choice 1,4,6

slim saddle
#

as in the numbers 1,4,6?

trail mango
#

yes

slim saddle
#

isn't that consecutive tho?

trail mango
#

1 and 4 and 6 are not consecutive

#

the blocks are what prevent the choices from being consecutive

slim saddle
#

so what do i do from there

trail mango
#

it is not too hard to count the ways you can place the blocks but i don't recommend doing it like this on second thought

ancient basalt
slim saddle
#

mhm

ancient basalt
#

i have no clue how to go further

#

maybe if we choose 1 then we can choose the second number from 3-10

#

if we choose 2 then 4-10

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(i have no clue if this will even work)

trail mango
# trail mango

if you want to count cases like that you should use a visual aid like this

#

that was going to be my not so nice way of doing it

slim saddle
#

wait so is the # ways to place the blocks 9 ways

trail mango
#

should be more than that

slim saddle
#

can the blocks be separate? i.e. (1,3)

trail mango
#

(1,3)?

slim saddle
#

like place 1 and 3 together as one block

slim saddle
#

im like actually lost

#

<@&286206848099549185>

ancient basalt
#

is this an olympiad question?

slim saddle
#

k just found the solution it's 10C3-9C1*8+8

slim saddle
ancient basalt
#

oh alr

slim saddle
#

👍

trail mango
#

that's (10-3+1) choose 3 hmmge

#

it seems they did not count it very elegantly if they wrote the answer as 10C3-9C1*8+8

slim saddle
trail mango
final saddleBOT
#

@slim saddle Has your question been resolved?

final saddleBOT
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delicate fiber
final saddleBOT
delicate fiber
#

Im getting 1/e^2 when it should be 1/e, anyone see a mistake?

#

whole q btw

misty torrent
#

As you multiplied by 2 in this equation both sides

#

you wrote integral 0 to pi directly because of part ii

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but for right side it is 2 * integral 0 to pi/2 right?

#

And you did..

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@delicate fiber

delicate fiber
#

Ohhh crap

#

Thats why

#

Thanks

#

.close

final saddleBOT
#
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final saddleBOT
#
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glass ember
#

hello

final saddleBOT
glass ember
#

if riding a toy car for A minutes cost B dollars. How many mintues would you be able to ride for C dollars?

robust fulcrum
#

see

pliant shore
robust fulcrum
#

do this with unitary method