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12:00 AM
@Link stop guessing in the dark! You should have atleast some light to wander around!
 
i get it not
sin3x = sin(x+2x)
 
user19161
@Link sin2A=sin(A+A) and sin3A=sin(2A+A). Use these together with the addition formula.
 
= sin x cos 2x + sin 2x + cos x
is that right?
 
@Bitrex Just a min. I am working on it. I do not guarantee a solution though.
 
user19161
The problem with math teachers these days is that they throw formulas around without explaining how they work so students are left confused.
 
12:01 AM
Supposedly, $\sum_{n=0}^{\infty}\frac{N!N!}{(2N)!} = \frac{4}{3} + \frac{2\pi}{9\sqrt{3}}.$
 
yes
:C
 
user19161
Not all math teachers suck, but most of them do.
 
@Bitrex Do you wanna prove that?
 
$\sum_{n=0}^{\infty}\frac{N!N!}{(2N)!} = \sum_{n=0}^{\infty}\frac{N!(2N -N)!}{(2N)!} = \sum_{n=0}^{\infty}\frac{1}{2N \choose N}$ Maybe?
 
@PeterTamaroff I'm trying to think up an approach to think about proving it :)
 
user19161
12:02 AM
So @link first work out sin 2A from sin (A+A) and then use that to work out sin 3A.
 
okay
sin(2x) = sin(x)cos(x) + cos(x)sin(x) = 2 sin(x)cos(x)
 
user19161
And you may ask where the addition formula for sine comes from. Well, from geometrical considerations, and that is a little difficult to prove.
 
is that work right?
 
user19161
@Link Yes.
 
yay
then i would do sin x + 2 sin(x) cos(x)?
 
user19161
12:06 AM
@Link Well, apply the addition formula to sin(2x+x).
 
sin(3x)
 
@Bitrex Probably this will help.
 
everything comes from euler's formula, geometry can get stuffed!
 
or you mean the sum formula?
 
user19161
@Link Whatever you call it.
 
12:07 AM
so sin (2x + x ) = sin 2x cos x + sin x cos 2x
 
user19161
@Link Yes. Now you need to know what is cos 2x. That can be found from cos (A+B)=cosAcosB-sinAsinB.
 
okay
so then it comes out to sin 2x cos x + sin x (cos x cos x - sin x sin x)
like that?
 
user19161
@Link NO.
 
hmm
 
user19161
cos 2x = cos (x+x)
 
12:12 AM
arrgh
oh yea
:C
 
user19161
Like I said, read your textbook 9000 times first.
 
sin 2x cos x + sin x (cos x cos x - sin x sin x)
:D
 
user19161
OK, now expand everything out.
 
okay
 
user19161
Once this stupid teacher said she must "drill" the students. But drilling them with all the wrong things makes them learn the wrong things.
 
12:15 AM
sin 2x + cos x + sin x cos^2 x - sin^3 x
i think i did tht right
 
user19161
So they can move symbols around, but without understanding the reason the movements all become wrong later on.
 
i agree
i had to relearn deriatives the hard way
 
user19161
@Link How did the times become a plus?
 
i could do them
just didn't know why
whuch one?
 
user19161
@Link Look carefully.
 
12:17 AM
it goes sin2x cos x + sin x ( cos^2 x - sin^2 x) = sin 2x cos x + sin x cos^2 x - sin^3 x
 
user19161
@Link Exactly, which is not what you wrote.
 
ooh
:c
do i expand the sin out now?
 
user19161
2 mins ago, by Link
sin 2x + cos x + sin x cos^2 x - sin^3 x
 
oops
 
user19161
@Link You expand the sin 2x now.
 
okay
i got it now
thanks
 
user19161
@Bitrex So true. I hate some of these teachers. I talked to them and they acted as if I know nothing about mathematics when it is they who know nothing.
 
user19161
@Link We are not done yet.
 
@Bitrex I think I can help
 
@PeterTamaroff I'm listening.
 
user19161
12:22 AM
@JayeshBadwaik Hehe.
 
@JayeshBadwaik No, you're not.
 
@PeterTamaroff I am. Serious.
 
user19161
@JayeshBadwaik I think we usually don't abbreviate that.
 
@JasperLoy Thanks.
 
user19161
@link Have you been kidnapped?
 
12:24 AM
@JayeshBadwaik OK
 
user19161
@PeterTamaroff Wrong line.
 
@JayeshBadwaik Consider $a_n=4^n {2n\choose n}^{-1}$
 
Okay.
 
Now, express $a_{n+1}$ in terms of $a_n$.
You'll need just a little manipulation.
 
hhh
Am I understanding the term "positively definite" correctly?
 
12:27 AM
$${a_{n + 1}} = \frac{{2n + 2}}{{2n + 1}}{a_n}$$
 
Well $a_{n+1} = 4\frac{(n+1)^2} {(2n+2)(2n+1)}$
 
@JayeshBadwaik Whuuuu?
 
@PeterTamaroff $a_{n+1} = 4^{n+1} {2n+2 \choose n+1}^{-1}$
 
hhh
12:29 AM
(the arbitrary $\bar x$ is defined inside an unit ball, can the norm be arbitrary?)
@PeterTamaroff To me?
 
@hhh Please do not post long images in between conversations? It destroys the continuity for other people.
 
hhh
-
 
@hhh Yup.
 
@hhh Nope, sorry.
@JayeshBadwaik $$\frac{{2\left( {n + 1} \right)}}{{\left( {2n + 1} \right)}}{a_n} = {a_{n + 1}}$$
This can be written as:
 
@PeterTamaroff yup, we have written the same thing.
Except I did not write $a_{n}$
Anyway, I agree with you.
 
12:32 AM
@JayeshBadwaik OK, now we write that as
$$2\left( {n + 1} \right){a_{n + 1}} - {a_{n + 1}} = 2n{a_n} +2 {a_n}$$
 
Okay.
 
user19161
I think Link has been kidnapped. Send in the special force!
 
@JayeshBadwaik Now consider the generating function $A(x)$ of $a_n$
This means
 
@PeterTamaroff Ahh.
 
@JayeshBadwaik You'll get a diff eqn
 
12:33 AM
Hmm. Yup.
 
@JayeshBadwaik I leart that easy case from this here
 
okay.
Yup, so we solve for the function and then put in the appropriate value of $x$ to get the summation of $a_{n}$. Neat.
 
@JayeshBadwaik Yeah =)
 
@PeterTamaroff I somehow got stuck in the ratio and was trying out convergence tests to first determine whether the sequence actually converges or what.
It obviously does though. Since the term decreases exponentially fast.
 
@JayeshBadwaik Hmmm. I want to prove that if $a_n$ is Cauchy then it converges. Should it be too long of a proof??
 
user19161
12:40 AM
@PeterTamaroff You need completeness of course.
 
@PeterTamaroff It actually depends on completeness of the space.
 
@JayeshBadwaik You should use Wallis' approximation.
@JayeshBadwaik I'm on $\mathbb R$.
 
@PeterTamaroff Yup. I used that.
 
@JayeshBadwaik Oh, OK.
 
@PeterTamaroff It is not a long proof. Quiet simple actually.
 
user19161
12:41 AM
@PeterTamaroff Depends on what theorems you already have.
 
@JasperLoy Bolzano Weierstrass, Monotone Conv.
 
user19161
@PeterTamaroff Did we do this before? We can just use the fact that every sequence in R has a monotone subsequence. That leads to a neat proof.
 
@PeterTamaroff You should be able to do it on your own then. Its quiet concise then.
 
user19161
@JayeshBadwaik See my above remark. It is the most beautiful proof ever.
 
@JasperLoy Ever?
 
12:45 AM
@JasperLoy Yup. That is how I did it.
 
user19161
@PeterTamaroff Yes, to me. Beauty is in the eye of the beholder.
 
@PeterTamaroff By now you should have realized that @JasperLoy talks in hyperbole.
 
user19161
@JayeshBadwaik Yes, for instance, 9000.
 
@JasperLoy Well, Spivak does this: Proves every Cauchy sequences is bounded, then prove it has a conv subsequence. Then he asks me to prove that if a subsequence of a Cauchy sequence converges, the original sequence does. I think I can do it. At least, I can picture the idea.
 
user19161
@PeterTamaroff Well, the convergent subsequence can just be taken as the monotone one I speak of. Alternatively, use the ones that go to limsup or liminf.
 
12:52 AM
@JasperLoy Yeah. Now I'm thinking: Say $\{a_{n_j}\}$ is the subseq.
 
user19161
@PeterTamaroff I will give you the hint for the monotone proof.
 
Then there is an $\ell$ such that for every $\epsilon >0$, there is an $N$ such that $$|a_{n_j}-\ell|<\epsilon$$ whenever $n_j >N$
@JasperLoy Shhhuuuuuuush!
2
 
hi @Charlie
 
@skullpatrol Hello!
 
$$\left| {{a_n} - \ell } \right| < \left| {{a_n} - {a_{{n_j}}}} \right| + \left| {{a_{{n_j}}} - \ell } \right| < \frac{\epsilon}{2} + \frac{\epsilon}{2}$$
@JasperLoy Done!
 
user19161
12:56 AM
@PeterTamaroff Yes, that is the idea and where the Cauchiness comes in. Now do you know how to get the monotone subsequence?
 
@JasperLoy I already got it.
 
user19161
@PeterTamaroff OK, well done. Can I befriend you?
 
@JasperLoy Maybe.
 
@JasperLoy You have to be on fb first.
 
user19161
Hey guys, do you know why you will never find me on FB now?
 
user19161
12:57 AM
Because I have no FB account! QED.
 
user19161
@peter What is your proof of the existence of the monotone subsequence?
 
@JasperLoy I show the Cauchy sequence is bounded. Not monotone subsequence, but CONVERGENT subsequence.
 
user19161
@PeterTamaroff Ah OK. Want to hear the other proof?
 
@JasperLoy The more the merrier.
 
user19161
@PeterTamaroff OK, now we want to show that every real sequence has a monotone subsequence. Call a term in the sequence a peak if it is greater than or equals preceding terms. If a sequence has infinitely many peaks, we have an increasing sequence. If it only has finitely many, we have a decreasing sequence.
 
1:01 AM
@JasperLoy That is how Spivak does it!
@JasperLoy But it is a little informal for my taste.
=O
 
user19161
@PeterTamaroff Wonderful. And of course, you know that a monotone sequence converges if and only if it is bounded!
 
@JasperLoy Yeah.
 
@jayesh you're in my ears and in my eyes
 
user19161
@PeterTamaroff Now I can be your friend. =)
 
@Charlie I am not penny lane! :-)
 
user19161
1:02 AM
@Charlie OMG.
 
@JayeshBadwaik \o/
 
user19161
Is Jayesh and Charlie getting married soon?
 
Do you wanna go to the wedding?
 
user19161
Maybe.
 
Why?
 
user19161
1:04 AM
Why? Why not?
 
I'm not going because I'll start crying :(
 
user19161
@skullpatrol Why? Is it because you want to marry one of them instead?
 
Why? Why not?
 
@jayesh are you reading this???
 
@Charlie yeah.
 
user19161
1:07 AM
I think skullpatrol and anon should get married. It will be an anonymous wedding. =)
4
 
@JayeshBadwaik did you rest?
 
@Charlie 3.5 hours. No worries, will sleep later.
 
@JasperLoy I think Jasper Loy and Good Will Hunting should get married. It will be a match made in heaven :-D
 
@JayeshBadwaik ok.i may sleep...
soon
 
user19161
@skullpatrol Now that is just rubbish!
 
1:09 AM
@Charlie Okay. good night!
 
user19161
I hate it when people star and then unstar my message.
 
@JayeshBadwaik i listened to 4 Beatles album
 
@JasperLoy You once said you're here to take out the garbage.
 
user19161
@skullpatrol That is because I am Will Hunting. How can I marry myself? Duh.
 
@JayeshBadwaik Night!
 
1:11 AM
@Charlie Nice. I got your octopus. Same here.
@Charlie good night.
 
@JasperLoy You are?
 
@JayeshBadwaik :DDDD
@JayeshBadwaik It will be a good night!
 
user19161
@skullpatrol Yes, I am. I am not Matt Damon. I am Will Hunting. QED.
 
@JasperLoy I thought you were Ben Affleck.
 
@JasperLoy Thanks for the information.
 
user19161
1:12 AM
Wait. Who is sleeping, Jay or Charlie?
 
@JasperLoy Charlie. It is morning here.
 
user19161
@JayeshBadwaik Do you celebrate Deepavali?
 
@JasperLoy Yup. It is one of the two of the festivals I always look forward to.
 
user19161
@JayeshBadwaik And the other one?
 
The other is Holi.
 
user19161
1:17 AM
Not heard of here.
 
user19161
Is that like Thaipusam?
 
No.
It is more like Baisakhi.
It is the the occasion of crop harvesting.
 
user19161
It's quite scary to see people piercing themselves.
 
@JayeshBadwaik What festival do you not look forward to?
 
user19161
I would not even want to wear an ear ring if I were a girl.
 
1:19 AM
@skullpatrol We have around 30-50 festivals in here. I cannot look forward to everyone of them!
 
user19161
I always look forward to Christmas and New Year's Day, just because of the mood.
 
There are three or four which I observed diligently. Rest, I do not pay much attention.
@JasperLoy Festivals are always about the moods.
 
I don't like Halloween.
 
user19161
I think I will skip all horror movies now.
 
But you like vampire movies.
 
1:21 AM
@JasperLoy Okay, so power is gone, I might sign out soon. Bye. Good day!
 
user19161
@JayeshBadwaik See you.
 
Or hope the power comes back in less than 10 minutes.
 
@JayeshBadwaik Do you have anything similar to Halloween?
 
@skullpatrol We have a festival for the dead, but it is quite formal and all. No funny stuff and not a big deal actually.
For children's fun, we have other festivals like Kojagiri among others.
 
@JayeshBadwaik So there is a festival for every mood?
 
1:27 AM
@skullpatrol Yes.
 
@JayeshBadwaik Combined with each age group?
 
There is a festival for appreciating the eldest sibling in the family since he has to deal with first-time and hence inexperienced parents etc etc.
@skullpatrol yup.
Most of them are not big deal. You would not find people stopping their work on every one of them.
 
Are there festivals for men only or women only?
 
There are some important ones, but others are taken in stride.
@skullpatrol Hmm. Not really. There are special festival(s) (I am not sure if there are more than one) for women, but men are included there too.
 
hi @jeighjoans
 
leo
1:38 AM
@PeterTamaroff hola!
 
Te perdiste la diversion @leo
un poquito de secuencias de cauchy por aqii y por alla
 
leo
@PeterTamaroff estaba viendo tu pregunta en el main
que, ya salió?
 
ahh la de la aritmetica de la secuencia?
 
leo
si
 
si salio que??
 
leo
1:52 AM
@PeterTamaroff que si ya pudiste demostrarlo
 
ahh... no esta casi twrminada la demostracion? Que crees?
 
leo
@PeterTamaroff I'm not sure that you always con choose the $N$ and $n_0$ properly. However I don't know how to explain why
 
leo
@PeterTamaroff perhaps I'm wrong
 
Como lo harias vos?
 
leo
2:02 AM
@PeterTamaroff igual que tu. Llegaría al punto en que está el post y entonces no sabría como seguir
 
@leo =P
 
leo
@PeterTamaroff tengo otra forma, pero solo sirve para $a_n$ monótonas
 
@anon Is there anyway to format your link:
5 Main Chatroom Etiquette Rules | Latex Support for Chat - 5h ago by anon â–¼
into the title description:
Associated with Math.SE; for both general discussion & math questions alike. Please see meta.math.stackexchange.com/questions/3890/… for the rules ("ChatJax" link contained therein).
 
My answer is the same as last time: I don't know how to format links in the chatroom description. (I still haven't even looked into it.)
 
@anon Hey
 
2:04 AM
also I had no idea that triangle was copypastable
 
ah, cesaro sums
pretty sure I have an answer for that over $\Bbb C$ somewhere
 
@anon No, Cesàro sums are different.
 
how so?
 
leo
How
 
2:07 AM
They are $$\frac{s_1+s_2+\cdots+s_n}{n}$$ where $s_n=\sum_{k=1}^na_k$
 
oh right
 
This is just the arithmetic mean.
One is the average of the terms, the ohter is the average of the partial sums =)
That's a nice way to remember it.
 
leo
@PeterTamaroff you can take $a_k=b_{k+1}-b_k$ with $b_1=0$ and then it is a Cesàro sum
 
@leo Well, yeah.
 
@PeterTamaroff I have to back AD's approach, it's more or less what I had in my answer I'm not going to bother finding.
 
2:10 AM
@leo But it is not the original sequence =P
 
You can of course rephrase it without limsups if you want.
 
leo
@PeterTamaroff you can fix it
:-)
 
n(n+1)(2n+1)/6
 
leo
that one
 
@leo LAWL =P
 
user19161
2:14 AM
Hmm, I am trying to think of a really short proof for Pedro.
 
user19161
I seem to have dreamed about this 9000 years ago.
 
Maybe you're dreaming about this right now.
 
I have to sleep now! @leo I'm almost finishing with Spivak's book!
Then I'll go on with Algebra, maybe.
 
user19161
@PeterTamaroff Well done!
 
leo
@PeterTamaroff that's great!
 
user19161
2:17 AM
@peter Is the converse true?
 
@JasperLoy Too late for mindgames!
 
user19161
@PeterTamaroff OK, I will see you in your dreams.
 
welcome back @JayeshBadwaik
 
I need to get the cymbals monkey going in my head now..
 
@PeterTamaroff you solved every problem from the book?
 
2:19 AM
@JayeshBadwaik Nah, but I usually worked out the relevant ones.
I still have lots of exercises to solve, though!
LOTS OF THEM!
 
user19161
@PeterTamaroff Good, good!
 
user19161
@PeterTamaroff That monkey looks a little like you.
 
How can you say you're finished with the book?
 
@PeterTamaroff Hmm. I thought you solved every one of them. Then I would have given you the title of superperspicacious.
 
@JayeshBadwaik I'll let you know when I do
@skullpatrol " I'm almost finishing with Spivak's book!"
 
user19161
2:22 AM
@PeterTamaroff Almost means except for a finite number of pages.
 
@PeterTamaroff about your cesaro sums thing, I think you have got it correct, the stolz cesaro thing.
Do you want verification for the upper part?
 
@JayeshBadwaik Yes! Please!
@JayeshBadwaik It is an awesome theorem to have at handy, like LH-
 
@PeterTamaroff Yup! Totally agree.
 
user19161
@JayeshBadwaik Also very beautiful.
 
user19161
Ah, I think I am going to bed as well. Over and out!
 
2:27 AM
@JasperLoy dude, self-study is hard. You not only have to study, you also have to find out what to study (which is infinitely difficult). You can study single books and get stuff from one direction (mainstream stuff), but so many things are not given in a single book! And things which are not mainstream fall through the cracks.
 
user19161
@JayeshBadwaik Better than studying at crap places under crap lecturers and syllabi. You know what I am thinking of...
 
@JasperLoy Hmm. Prolly.
 
user19161
@JayeshBadwaik Hehe. But if you stick to my nine holy books, you can't go wrong.
 
@JasperLoy Blah. I think even they would miss something or the other. Rudin already misses some stuff. Point is you cannot focus on a single book.
 
user19161
@JayeshBadwaik Actually, self study to me is not hard. Solving my life problems is hard. Like I said, if not for them I might have won the Fields Medal by now. =)
 
2:30 AM
Sanity check please! It is too late...
 
user19161
@JayeshBadwaik Yes. My point is, every book will leave out something important.
 
user19161
@PeterTamaroff You should be in bed now dude.
 
@JasperLoy Self-study is not hard to me either. But you lose out important stuff, which it is not possible for you to know is important or even to know it exists.
 
@JasperLoy Yeah. Bye.
 
user19161
@JayeshBadwaik I knew important stuff precisely because I ignored the lectures and lecturers...
 
2:32 AM
@JayeshBadwaik That's why we need to research!
 
@PeterTamaroff research? as in?
 
user19161
@JayeshBadwaik Meaning read up on your own dude.
 
@JasperLoy hmm. Okay. like that. Yup! You are correct.
 
user19161
@JayeshBadwaik I have looked through 9000 course syllabuses and 9000 books. Even though I don't know the math now, I know about the math.
 
@JasperLoy Hmm.
 
user19161
2:34 AM
@JayeshBadwaik But your Artin book is a great choice. In particular it covers geometrical aspects not treated elsewhere.
 
@JasperLoy Yup, that i observed. It is really nice in that aspect.
Also, it has really good miscellanous questions which are like exploration to other areas sometimes not covered in book.
 
user19161
The Fraleigh book I really dislike, even though it is very popular too. I dislike Herstein too.
 
user19161
I do like the Artin book but I don't have a copy nor am I gonna read it now.
 
@PeterTamaroff Seems correct to me. your solution. of that DE.
@JasperLoy hmm. It is noon at your place right? You sleep at this time? Don't you feel uncomfortable due to excessive body heat?
 
user19161
@JayeshBadwaik Well, when the mind is troubled, the body is immune...
 
2:39 AM
@JasperLoy I would have thought otherwise. When the body is healthy, it stabilizes your mind and makes it less troubled.
 
user19161
@JayeshBadwaik I am weird. Nature's laws do not apply.
 
leo
@PeterTamaroff what is asked in your post follows from a theorem by Toeplitz. No Wikipedia link to that theorem
 
@JasperLoy :P
@leo which question I mean?
 
leo
2
Q: If $a_n\to \ell $ then $\hat a_n\to \ell$

Peter TamaroffI need some help to finish this proof: THEOREM Let $\{a_n\}$ be such that $\lim a_n=\ell$ and set $$\hat a_n=\frac 1 n \sum_{k=1}^na_k$$ Then $\lim\hat a_n=\ell$ PROOF Let $\epsilon >0 $ be given. Since $\lim a_n=\ell$ , there exists an $N$ for which $$\left| {{a_n} - \ell } \right| <...

 
user19161
@jayesh I am planning to study six of the nine books next year as mentioned, and also aiming for complete recovery by end of next year. But these are just plans. I don't know what is gonna happen to me...
 
2:44 AM
@JasperLoy You will succeed in your recovery and consequently mathematics.
 
user19161
@JayeshBadwaik Yeah, we might even meet in grad school one day...
 
@JasperLoy Hopefully!
 
user19161
@JayeshBadwaik Anyway, with regard to Indian food, I think I like masala tosai.
 
@JasperLoy It is my favorite too. Masala dosa and idli sambhar.
 
@leo interesante! Toeplitz??
 
user19161
2:50 AM
@JayeshBadwaik There is another book that treats the geometry of algebra, online for free. It is Goodman's Algebra.
 
user19161
At this rate, Pedro will never go to bed.
 
@JasperLoy okay. thanks!
 
leo
@JayeshBadwaik almost. It something similar. The one I say changes the first hypothesis by the boundedness of $(a_{nm})_n$ for each $m=0,1,\ldots$
@PeterTamaroff yep
 
@leo link??
 
user19161
@peter Check out Goodman's Algebra too. It is very good and it is online.
 
leo
2:53 AM
boundedness of columns
@PeterTamaroff let me see
@PeterTamaroff follows from this one
@PeterTamaroff can you see it?
 
3:18 AM
achh
 
 
3 hours later…
5:53 AM
Can anyone believe Einstein's "God Letter" is being sold on ebay?
What's next, Gauss's unpublished theorems on Craig's List?
 
@skullpatrol I hope so!
 
@JonasTeuwen Me too :-D
The opening bid for the letter was $3 million...
@JonasTeuwen I was just reading Gauss's diary was only 19 pages long.
 
6:14 AM
"Did maths today"
 
"Discovered something."
That's roughly 1/3 of a page for every year or 1 paragraph/year.
 
6:42 AM
@JonasTeuwen Silly question, but how can I update an information of file from google books etc by just entering the ISBN of the book in Mendeley?
 
6:57 AM
@JonasTeuwen Look at Tellico. It probably does everything that mendeley does and does it better. Except for syncing though. However, I do not use syncing as of now, so its no bigggie. And I guess, if I want to, I will just sync a git repo for the library.
 
7:55 AM
@JayeshBadwaik heya
 
8:13 AM
@N3buchadnezzar Hi
 
Soup dawg?
 
trying to wrap my head around some linear algebra.
What about you?
 
trying to wrap my head around some linear algebra.
 
@N3buchadnezzar :P :P nice.
 
8:26 AM
hmm
 
Nice hyperbolic challenge at the end.
 
hyperbolic challenge gut punch
 
Indeed a bit below the belt, in my opinion.
 
8:48 AM
hi @Bitrex
 

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