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7:13 PM
"put over a common denominator"
 
hi chat
 
@BalarkaSen hi
 
7:32 PM
how are you
 
Alright. What about you?
 
good
 
 
1 hour later…
8:36 PM
Hi all.
Why can we express sine function as an infinite product? What factorization was that exactly?
 
9:03 PM
Glad to see you made it home safe and sound, @Semiclassic.
 
what about me?
 
hi @Alessandro, stranger :)
what about you, @MikeM?
 
you're not glad to see me safe and sound?
 
Of course not.
 
Hi all!
 
9:05 PM
Annoying when the OP removes his question after I take the trouble to comment. Presumably, my pointing out a chain rule mistake resulted in his knowing how to solve the problem.
Hi Simple
 
@TedShifrin I feel you
Say, could someone look at my answer here? It has two downvotes and I want some opinions on why so: math.stackexchange.com/a/1945547/272831
 
@TedShifrin thanks
still kind've sore from it
 
@Semiclassical Hey
You in the chat a lot it seems to me
And Weierstrass factorization is amazing
 
i guess so
 
@deostroll The exact expansion is used in one of Euler's solutions to the Basel problem
 
9:08 PM
"used" probably being the operative word there. there's a reason Weierstrass's name is attached to the factorization theorem.
 
@SimpleArt: So, I wish the OP hadn't used $n$ for a "tiny" number. But what he wrote is just wrong. He never divided the interval up into $n$ pieces. You're of course correct that he wishes to take a limit of a sum of $n$ things as $n\to\infty$. So set $\epsilon = a/n$. Don't choose an arbitrary $\epsilon>0$.
BTW, @Simple, you should update your profile. I assume that by now you've studied and learned some calculus :P
 
Oh, right!
@TedShifrin ;) thanks for the reminder!
Idk, tbh...
 
I should probably update my profile eventually, but w/e
 
I haven't been 'learning' in my calculus class
 
9:11 PM
The original question is just plain wrong. You're trying to turn it into a reasonable question, but I would rewrite your approach. ...
 
All I need to do is trig substitutions and I already know everything else.
 
Why haven't you been learning? Just too plug-and-chuggy?
 
@TedShifrin Sure, thanks
 
Do you know Spivak's masterpiece Calculus?
 
@TedShifrin I already learned most of Calc I-II
No, I haven't sat down to read any good books yet
 
9:12 PM
You should get Spivak and do his exercises. Fantastic book. And then, of course, I recommend my own book as the multivariable/linear alg. sequel :P
 
@Semiclassical which came first, Euler's factorization of sine or Weierstrass?
@TedShifrin self-promotion all the way huh? XD
 
We should check dates, but I'm pretty sure Euler did it "seat of pants" first.
 
Hey guys if anyones good with elementary-number-theory I would be very happy if u could help with this one math.stackexchange.com/questions/1943982/…
 
well, considering Euler was dead before Weierstrass was born...
 
@SimpleArt Yup. I also contributed more than hundred exercises to the latter editions of Spivak.
@Semiclassical I've always been terrible at memorizing things in history. But I thought so.
 
9:14 PM
@Semiclassical Exactly XD
 
admittedly, I had to check to be sure.
 
:P
@TedShifrin Same. History my weakest subject
 
but Euler died before 1800, and Weierstrass was born after 1800
anyways, rigor definitely came way after Euler
 
@AjaxEdm You ought to learn MathJax
@Semiclassical Euler is magic
@AjaxEdm Sorry mate, but I can't help with that kind of stuff
 
@SimpleArt Sorry i'm new here need to get first used to it :(
 
9:15 PM
eh. Ramanujan was magic. Euler was creative and prolific.
 
@Ajax: This is not elementary number theory. This is basically understanding foundational questions. You should change the title and the tag. The first condition is called the well-ordering principle in $\Bbb N$.
 
Ramanujan was such a cheater with his dream goddess
 
@Semiclassical XD All the awesome mathematicians are gods in my eyes.
 
@TedShifrin hmmm okj
 
9:18 PM
it's also worth having some historical perspective. it's basically impossible to have an Euler or a Gauss now, simply because there's not as much left to discover.
 
@mercio Honestly, I feel you shouldn't be able to determine "OH!!! That's the smallest number representable as the sum of two cubes!" in a few minutes in your head.
@Semiclassical I feel that way too.
 
and, plus, there's just a lot more mathematicians now than then.
 
@Ajax: I would also recommend (to make it less confusing for you and for every one else) that you use capital letters for sets and little letters for elements of sets.
 
I think he had a LOT of xp
 
same as how there'll never again be anyone like a Cronkite when it comes to the news
 
9:19 PM
@Semiclassic: There are still folks like that (admittedly, Erdös has died, but still ...).
 
(I pick that as my touchstone because we listened to an audiobook biography of him during the long drive)
 
@TedShifrin Well thats the problem the prof gave us the exercice like this
 
Say, if anyone here wants some good laughs...
124
Q: Do good math jokes exist?

RandomblueHave a good joke? Share. I know this is subjective, but the principle "should be of interest to mathematicians" trumps. (I hope.)

 
I don't like your professor, @Ajax. :)
 
@TedShifrin eh, even he didn't have the same sort of universal scope
 
9:21 PM
@TedShifrin well me neither ;) well i think i got part 1) done I'm just struggeling with the second part of the question the most proof that [3] implies [2]
 
Oh, of course, @Semiclassic. I just meant divine inspiration in elementary number theory and combinatorics. Not my sort of stuff, anyhow.
 
ahh
I remember someone referring to Poincare as the last 'universal' mathematician
 
I don't see why 1) implies 2), @Ajax. Why couldn't the set $A$ in 2) be the set of even positive integers?
 
@Semiclassical Math is really crazy. How do I learn all of it in time!
 
I dunno, @Semiclassic. It's hard to rule out some broad, brilliant 20th century people.
 
9:23 PM
Well 1) is just all sets T which are subsets of N so that they have a smallest Element
and 2) is the same but with all subsets with Z included
 
read lots of books, work on lots of problems, and talk/listen a lot to knowledgeable people
 
So we could argue they are equivalent
 
then repeat and repeat and repeat
 
@Semiclassical :( I want more knowledgeable math people on the high school level
 
Talkative room today. I'm sleepy.
 
9:24 PM
No, he still gives natural numbers in 2), @Ajax.
 
then focus on the first two :)
 
@MikeMiller Hi!
 
Oh, sorry, I hate the letter Z.
 
@Semiclassical Hm, no of any list of good reads?
 
9:25 PM
@TedShifrin Why?
 
i'm not the person to ask on that
 
Because I think it means integers.
 
pft, ok
 
N for naturals, Z for integers
 
@TedShifrin I'm pretty sure that's what it means..?
Yeah, what he said
 
9:25 PM
@Ajax: Is the statement 2) including the conclusion that $A=\Bbb N$?
 
i have to say, the question as written is pretty hard to read.
 
Is statement 2) that if we define $A$, then $A$ must be all of $\Bbb N$?
It's horrible, @Semiclassic.
This must be how my students felt for 40 years :P
 
@Semiclassical Maybe we should learn html
lol
XD
 
Hmmm now im getting confused
xD
 
9:27 PM
@TedShifrin Mathjax is beautiful.
@TedShifrin Tell him what \Bbb means
 
I have been using LaTeX since 1990 or so, @Simple.
 
"[1] Is T a not empty subset of the natural numbers N, that means their exists an X ∈ T, that X ≤ Y is fulfilled for all Y ∈ T." Is that a literal transcription?
 
oh $\Bbb N$ is just the set of natural numbers.
 
Damn i have no clue why this is included in my linear algebra class
 
@TedShifrin wow, SE that old? or just Latex in general?
 
9:28 PM
@Ted hi! I saw only now that you greeted me earlier
 
TeX and LaTeX are older than that. SE is young.
 
thought so
 
Latex goes back a ways, and Mathjax at the user level is just Latex
 
@Ajax: To get some logical structure for proofs established, but I think it has no business in a linear algebra class. I taught/required plenty of proofs in that course without this.
Heya @Alessandro. Glad to know you're still alive :)
 
I want to have my computer render MathJax on its own whenever I type
 
9:29 PM
@Ted I'm glad to know that too!
How are you?
 
"If $T$ is a non-empty subset of $\Bbb N$, then there exists $x\in T$ such that $x\leq y$ for all $y\in T$."
 
Ha ha ... you're so funny :)
 
@Alessandro Good, you?
 
Is that how it should be read?
 
@TedShifrin Well i could understand this in number theory but not here
 
9:30 PM
So 1) is just the standard well-ordering of the natural nubmers, @Semiclassic.
 
Right.
 
No, @Ajax: It's really an intro to higher math class where you deal with all sorts of proofs, induction, etc. That's where this belongs. But, honestly, it's too confusing to be anywhere. Go bug your professor.
 
Huh
 
I still don't understand. If 2) includes the conclusion that $A$ is all of $\Bbb N$, then I don't see why it's even correct. And 1) does hold in $\Bbb N$. So they're not logically equivalent statements.
 
Was reading about well ordered sets and what they were
So is $\mathbb R^+$ a well ordered set?
@Danu Hello!
 
9:31 PM
No.
Not with the standard ordering.
 
are you guys talking about the equivalence between the well ordering principle and the (2 forms) of the induction principle?
 
@TedShifrin well how could i logically proof it as the same if A=N doesnt count to the statement
 
Well-ordered means that any non-empty subset has a least element, @Simple.
 
Biking home now... I'll be back in half an hour for more math :)
 
@TedShifrin Ah, thought so? at least on an intuitive level.
 
9:32 PM
Trying to translate 2), it seems to be:
 
@Danu yep thats why i meant to say before
 
@TedShifrin Including surreals, R^+ is well ordered?
 
*what
 
?
 
er, sorta?
 
9:33 PM
Well 1) is just all sets T which are subsets of N so that they have a smallest Element
and 2) is the same but with all subsets with Z included
This
 
@Danu That's how you should live life
 
@simple every subset of a well ordered set is well ordered (with respect to the original order restricted to that subset), I'm not familiar with the construction of the surreals, but they definitely contain a copy of $\mathbb{Z}$
 
For any $z\in \Bbb N$ and any subset $T\subset \Bbb N$ containing $z$, there exists $x\in T$ such that $x\leq y$ for any $y\in T$.
 
@Alessandro Nah, I'm interested in R^+
 
what's the least element of $(0,1)$ then?
 
9:35 PM
is that what's 2) supposed to be?
 
@Alessandro Oh no, R^+ not including 0 here
 
No, @Semiclassic. I believe you have to define the set $A$. And 2) is the claim that then $A=\Bbb N$. Otherwise, it makes no sense.
 
sorry, forgot to mention that
 
doesn't make any difference, what's the least element of $(1,2)$?
 
Is @BalarkaSen still around?
 
9:36 PM
@TedShifrin I'm trying to both define $A$ and claim that it's equal to $\Bbb N$ at the same time
 
Alessandro is right, @Simple. In $\Bbb R^+$, any open interval you choose fails to have a least element.
 
1...
 
@Semiclassical Isn't just the same as 1) Just the difference that 2) are the subset that include Z with a smallest Element
 
hm, ok
 
However, it's equivalent to the axiom of choice that you can put some ordering on $\Bbb R^+$ which is well-ordered.
 
9:36 PM
But I meant basically if R^+ itself was well-ordered
 
Totally NOT.
 
But surreals
 
What the hell is that?
 
@Ted it is equivalent to AC that you can well order every set, well ordering the reals doesn't require full AC I believe
 
shrug @Alessandro :)
 
9:37 PM
Extending the reals to include transfinites and infinitesimals in my mind
 
oh, definitely not well-ordered
 
In mathematics, the surreal number system is an arithmetic continuum containing the real numbers as well as infinite and infinitesimal numbers, respectively larger or smaller in absolute value than any positive real number. The surreals share many properties with the reals, including a total order ≤ and the usual arithmetic operations (addition, subtraction, multiplication, and division); as such, they form an ordered field. (Strictly speaking, the surreals are not a set, but a proper class.) If formulated in Von Neumann–Bernays–Gödel set theory, the surreal numbers are the largest possible ordered...
 
@Simple the surreals, as far as I understand, contain a copy of $\mathbb{R}$ so you can just pick a subset of the surreals containing only standard reals and that can fail to have a least element as we showed you before
 
I know about the hyperreals. I am not sure what the difference is.
 
@TedShifrin me neither
:/
 
9:39 PM
hmm ... damn
This is harder then i thought
 
@Alessandro Well, cool. Thanks
 
Anyhow, I have to get going. Have to go help 4th-7th graders with their math for 3 hours.
 
makes me think of things, like whether or not limit points exist
@TedShifrin Have fun :D
 
@TedShifrin do you agree with the sentiment expressed by my topology professor that "the only thing worse than thinking about [the foundations of] set theory is thinking about what numbers "really are""? :P
 
I wish I got to teach people math
 
9:40 PM
Oh, bye Ted!
 
Let me render it a bit differently: Let $A$ be the set of natural numbers $z$ such that, if $T\subset \Bbb N$ contains $z$, then there's some $x\in T$ such that $x\leq y$ for all $y\in T$. Then $A=\Bbb N$.
 
@ted bye!
 
@Danu What are numbers?
@SteamyRoot hey!
 
ohi
 
You know, it is a very strange thing conceptually understanding something without knowing what the hell the complicated symbols means
 
9:43 PM
@BalarkaSen your remarks just clicked!! Thanks
@SimpleArt who cares? :)
 
@Danu :'(
The people that say "WTH YOU USING 'N' FOR COMPLEX VARIABLES! WE USE Z, \mu, AND SOMETIMES X FOR COMPLEX..."
I've been yelled at more than once for this XD
 
@Danu can I ask you where are you studying in Germany? I'm thinking about doing my master degree there
 
And at the same time, I get upvotes for the right answer
 
@Alessandro Munich
@SimpleArt i agree that using n is a terrible idea
 
Oh, nice, I have a friend who studied physics there as an exchange student, he already told me a lot about Munich's uni :)
 
9:48 PM
Ok, maybe it wasn't "n", I think it was somewhere else...
but see? People do care
I wanna learn quantum physics when I grow up
and all the math too
 
it's standard notation to reserve $n$ for integer variables, it just makes your writing easier to read when you stick to usually accepted conventions
a more extreme example would be something like "let $x:\mathbb{R}\to\mathbb{R}$ be the function that maps $f$ to $f^3$, find $\frac{dx}{df}$, which is trivial of course, but painful to read
 
@Alessandro Yeah, I figured that out eventually. And k,p,q too. Way too many variables IMO
XD Quite funny
I mean, I can't help it if I've never taken any course using those variables. :( I want to take those courses though
Hm, any of you guys (and girls) have a favourite post?
 
anyway I'm going to sleep now, I have to get up early for classes tomorrow
bye
 
G'night
 
10:45 PM
So @BalarkaSen what you were trying to say is that I should view the $(\ell,0)$ elements as projectivized elements of $T_0\Bbb C^{n+1}$. This easily generalized to blowing up $\Bbb C^m$ because in that case the $\ell$ are all in the complement of $\Bbb C^m$, so we get exactly the projectivization of the normal bundle. Great.
 
hello
 
11:14 PM
I have a question - is there a way to get the integer part of sqrt(2)*x, while staying in natural numbers domain? So sqrt(2)*5, would be 7.
 
11:32 PM
@KeithYong It's called the "floor function"
In mathematics and computer science, the floor and ceiling functions map a real number to the largest previous or the smallest following integer, respectively. More precisely, floor(x) = ⌊ x ⌋ {\displaystyle \lfloor x\rfloor } is the largest integer less than or equal to x and ceiling(x) = ⌈ x ⌉ {\displaystyle \lceil x\rceil } is the smallest integer greater than or equal to x. == Notation == Carl Friedrich Gauss introduced the square bracket notation [ ...
 
I need hints
but then again I think it's just prove it's a subring stuff
 
Lol
Magical floor functions. what are we doing?
@KeithYong take the floor of that...
@usukidoll What are you talking about?
@AaronHall Hi
 
11:50 PM
Hi! :)
 
finishing this prntscr.com/cnkpqo
I was told for a to use definition of a subring on it
and then b is show two different definitions are equal
and c should come the same as part a... it's part b and c that I'm a bit stuck
 
Not my area of mathematics
sorry
 
so I should just wing it then :/
can't find that much on it online ughhh
 
Lol, sorry
you could try asking it as question on the main site
 
I'm not taking a risk of being downvoted
I leave it up to you then :P
 

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