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10:00 AM
@Sawarnik .ti eserver os
 
@ParthKohli reverse the block.
 
@Sawarnik kcolb eht
 
@ParthKohli Toidi si ilhok htrap.
 
@Sawarnik .toidi na si ilhok htraP*
 
@r9m, I AM RIGHT FOR SURE!!!!
 
r9m
10:03 AM
@Sush okay .. :) I have to rethink then
 
$\sum_{k=1}^n k^2\binom nk=n2^{n-1} + n(n-1)2^{n-2}$
 
@ParthKohli .BF no kcolb eht esreveR
 
@r9m See this
And $2^{n-2}n(n+1)=n2^{n-1} + n(n-1)2^{n-2}$@r9m
 
@Mike The summoning mechanism is a little buggy. At least it summoned me eventually.
 
r9m
@Sush OMG ... I forgot that when captain and fundraisers's positions can be interchanged as well so the answer is $\sum_{k=1}^n k^2\binom nk=n2^{n-1} + 2 {n \choose 2} 2^{n-2}$
thanks :D .. my bad
 
10:06 AM
Hi, @KarlKronenfeld, ☺
Your Alt technique is really fascinating!@KarlKronenfeld
@r9m, o ya! but i checked my answer at least 5 times manually! Then got that online calculator!
 
@Sush Hi
 
Bye bye everyone!
 
@Sush Glad you liké it. Though I certainly can't claim it as my own.
 
r9m
@Sush so 'execute/hang' me for wasting your time (sorry again)
 
@PedroTamaroff I hope I'm not included into "that" kind.
 
10:09 AM
@ParthKohli You are.
@r9m Nice idea :D
 
r9m
@Sawarnik ha .. as if you can lay your hands on me :P [Don ko pakadna mushkil hi nai ... ]
 
@Sawarnik That's bad. If people think I'm polluting the chat, I better leave.
 
@ParthKohli Oh, I may be joking.
 
@r9m You are of course not as intelligent and smart like him :P :P
@hawk What happened with the other inequality? I don't see any answers :p
 
10:21 AM
Greetings!
 
r9m
@Chris'ssis It's a Bird...It's a Plane...It's SuperSis .. Greetings :)
 
Greetings SuperSis!
Bye.
 
A nice series ... $$\sum_{n=1}^{\infty} \frac{1}{(2 n-1) (16 n^2-16 n +3)}=\frac{\log(2)}{2}$$
 
r9m
10:36 AM
@Chris'ssis wont partial fractions help ?
 
@r9m It would help I think.
 
10:58 AM
hiii
2 colouring algo is polynomial time
but k colouring is np because it is not known if input n can be solved in polynomial time, am i right?
 
 
1 hour later…
12:02 PM
@r9m How about finishing all without pen and paper? I can show you this is possible (using high school knowledge only).
 
12:19 PM
What integrals I have here now ... almost cry for pleasure ...
 
r9m
12:46 PM
@Chris'ssis wopap ? cool :) how ?
 
Why does $\frac{t - [t]}{t}$ tend to $O(1/t)$ ?
 
@r9m I let you think of it for a while.
 
1:24 PM
@N3buchadnezzar I'd say the first expression behaves like the second one as $t \to\infty$. This is what you meant I think.
In mathematics, big O notation describes the limiting behavior of a function when the argument tends towards a particular value or infinity, usually in terms of simpler functions. It is a member of a larger family of notations that is called Landau notation, Bachmann–Landau notation (after Edmund Landau and Paul Bachmann), or asymptotic notation. In computer science, big O notation is used to classify algorithms by how they respond (e.g., in their processing time or working space requirements) to changes in input size. In analytic number theory, it is used to estimate the "error commi...
 
2:22 PM
$$\frac{\displaystyle \sin^2\left(\frac{1}{2}\right)}{\gamma^2+1^2}+\frac{\displaystyle \sin^2\left(\frac{2}{2}\right)}{\gamma^2+2^2}+\frac{\displaystyle \sin^2\left(\frac{3}{2}\right)}{\gamma^2+3^2}+\cdots =\frac{\pi}{4\gamma}(\sinh(\gamma)+\coth(\gamma)-\cosh(\gamma)\coth(\gamma))$$
(newly created)
 
2:37 PM
there should be a search bar to search your own questions/answers
don't you agree?
 
2:47 PM
sometimes I can't find my own answers
 
$$ \int_0^{1} \sin(2\pi x) \left(\frac{1}{x^{1/4}} + \frac{1}{(x+1)^{1/4}} + \frac{1}{(x+2)^{1/4}}+ \cdots \right) \ dx = \frac{1}{2}\frac{\sqrt{1+\sqrt{2}} \space \pi^{1/4}}{ \Gamma\left(\frac{1}{4}\right)} $$
 
You must agrre after a while it becomes hard to navigate all your contributions
 
@user4140 :-)
 
so you agree?
 
@user4140 No, I'm a "nothing" in mathematics.
 
2:50 PM
huh?
I meant contributions to the site, not math
 
@user4140 No. There are lots of users with thousands of questions and answers far more interesting than ones of mine. Just search for them.
 
But still sometimes you might want to look up one of your previous answers right?
 
No. I'm involved in the process of creation too deeply and don't have time to look back. If wanna do that, I have my own database with problems and solutions.
@user4140 by the way, you can use the search field ...
 
yeh, but I never find it, if it where just my stuff it would be easier
 
I see.
 
3:09 PM
I just want to ask a very simple question about math. Finding mistakes in programming is called debugging, but what do we call finding mistakes in math?
@user4140 Can't you find your own answers here: math.stackexchange.com/users/33907/…
 
It's called math also @Kartik
@Kartik but it doesn't have a search option
 
@user4140 Use your browser's search (Ctrl+f)
 
but there are 111 pages
11*
 
@user4140 Oh... there must be some way to select number of elements in a page ... I am trying to find out.
@user4140 Just type in the search box user:me is:answer search terms
 
oh, thanks
 
3:26 PM
You're welcome.
 
3:50 PM
I need to find the image of $\cosh z$ in $x ≥ 0$, $0 ≤ y ≤ \pi/2$. I've convinced myself that it's $x ≥ 0, y ≥ 0$, but I'm not sure how to prove it.
Basically, I took the image of lines of the form $x + ia$ and found it's $\sinh (x) ⋅ \left(e^{-x}⋅cos a - i \sin (a)\right)$ which sort of suggests that I can express every complex number in that area.
I'm suspecting I'm missing something obvious.
 
4:17 PM
Can someone help me in understanding this:
The Monty Hall problem is a brain teaser, in the form of a probability puzzle (Gruber, Krauss and others), loosely based on the American television game show Let's Make a Deal and named after its original host, Monty Hall. The problem was originally posed in a letter by Steve Selvin to the American Statistician in 1975 , . It became famous as a question from a reader's letter quoted in Marilyn vos Savant's "Ask Marilyn" column in Parade magazine in 1990 : Vos Savant's response was that the contestant should switch to the other door. The argument relies on assumptions, explicit in exten...
 
4:27 PM
Sure. Can you be more specific? That is, what do you want to understand?
 
@GregRos I cannot understand the solution..
 
Have you looked at all the images there?
 
@GregRos No, I'm still reading it.
@GregRos I have seen them now
@GregRos But still didn't understand
 
The way that worked for me: There are 3 doors. You pick one. There is a 1/3 chance of the car being behind your door, and a 2/3 chance it's in one of the other two doors. The gamemaster opens one of the other two doors. You still have a 1/3 chance of being "right," but now the 2/3 chance is "concentrated" to that one remaining door. (I've got to run, so can't respond... but that's my $0.02...) :)
 
@anorton Then should the second probability not be 1/2
 
4:32 PM
What changed about your selection to make you suddenly have more of a chance of being right?
 
@anorton In the second chance you have to choose 1 door out of two?
 
You do have to choose 1 door out of two, but you have more information with which to make an informed decision. That is why the odds aren't 50/50.
Anyway--I've got to go. I'll be back later...
 
@anorton Bye
Ok... I got it!
 
5:07 PM
Hi! I have a little problem understanding definition of graded structures (rings, algebras). Namely there is a condition $R_m R_n \subset R_{m+n}$. But it is nowhere said what does $R_m R_n$ mean. Is it just a ring of pairs?
 
$R_mR_n$ is the set of finite sums of products $ab$ where $a\in R_m$, $b\in R_n$
 
thank you!
 
@Sawarnik I have posted the solution, I could not come online today, I could connect now, so I posted the solution.
 
And what does "Rarely if ever expressible as a ratio of integers" mean?
 
@Yrogirg Numbers that are expressible as a ratio of integers are called "rational." Thus, this room is rarely rational...
 
5:22 PM
@Yrogirg what is 'rarely if ever expressible...'?
 
:D
 
Hey, not sure if this is the right place to ask as it didn't seem like this would be worth posting a question, but could somebody help me to understand how to solve this integral: $$\frac{1}{\left(z^2+x^2\right)^{3/2}}$$
 
5:54 PM
Hi everyone, I'm working a combinatorics problem and I need some help
It asks, how many 8 letter strings of uppercase letters do not contain the string "ABC".
I have a feeling that I need to use derangements, but I'm not sure.
 
r9m
@alvonellos count how many has a "ABC" string .. and subtract them from the total number of 8 length strings possible with the alphabet
 
So, it's C(8, 26) - C(3, 26)?
That doesn't seem right.
 
6:12 PM
Hey. I actually have a question about Math Overflow, but I think the answer for Math SE would be the same, so I'm going to go ahead and ask here.
I asked a question on MO. So far, it has received exactly one answer, and that answer is incorrect (the author says so in a comment on the answer). I'm afraid of people looking at the question page and assuming that it has already been answered correctly.
What should I do here? Would it be appropriate to downvote the answer, or perhaps to ask the author to delete it? Should I edit it to add a notice saying it's incorrect? Or maybe I should just leave it alone?
 
you must challenge him to a duel for his honor
 
@TannerSwett You can add a notice to your question saying the only answer below is incorrect
and also, flag the answer for mod attention, requesting mod to delete it
 
@TannerSwett Personally I think whoever has even a slight interest in your question will click on it regardless of the number of answers. Unless it is too elementary, which I doubt.
 
@Mike I can't do that; that action requires 500 reputation on MO.
 
@TannerSwett it will also be good if you post the link to it in the mathoverflow chat room (or here if you like)
 
6:16 PM
If you want attention you can put a bounty on it, @TannerSwett
 
I don't think that does a whole lot on MO, but it makes it clear you're not satisfied with the current answer. But usually, the fact that a question doesn't have an accepted answer means the OP_ is not satisfied. I really doubt people who are otherwise interested in the topic wouldn't click on your question because of it.
 
@Mike i completely agree
 
@Mike Yeah, that makes sense.
 
btw, i came late today. lot of fiverr work (happy about it). did i miss any great fun?
 
6:21 PM
@TannerSwett The biggest trouble is that your question doesn't look like it's in one of MO's favorite niches.
You might tag it with better tags: none of those are "top-level" (the most used tags, usually the ones associated to an arXiv classification)
 
@TannerSwett you know there is theoretical computer science stack exchange
 
@Yrogirg I've already had the question moved from MSE to MO; it'd feel a little bit silly to move it a second time. But that might be a good option.
 
Finding more populous tags is definitely a good idea, though; only 95 questions are tagged formal-proofs, so it's unlikely more than a few people look through that list regularly. So the only people who find your question are those who are looking through old questions or those searching.
A lot of people use MSE and MO by only looking at questions in their favorite tags.
 
@Mike hAI
 
ok pedro's here i leave now
 
6:28 PM
Yeah, I think I'll try retagging the question. Thanks.
 
@Mike gives le finger
 
sup guys
I just proved the snake lemma
I'm contemplating suicide
 
wat
doesn't lang prove it?
=P
 
it's that bad
I haven't read Lang
this one is the best proof
 
6:47 PM
that little dude is an idiot
HOLD UP THAT'S NOT UNIQUE
also i hope he's in a homalg class
and bitching about diagram chases
@TannerSwett I suggest lo.logic
 
@FernandoMartin if only all math profs looked liked that?
did she call him "fuckface"?
 
@PedroTamaroff what about non-math proofs
 
@Mike what is that?
"non math proof"
 
OH
you said prof
 
@Mike YAS.
 
6:53 PM
no she called him Mr. cooperman
 
no
at the very end
when she leaves
@Mike "Oh no, Peter is objectifying women again!"
3
 
probably not
 
check
i left the time mark
 
haha she does
 
@FernandoMartin You're doing exercises from AM?
 
7:03 PM
Yup
I'm reading chapter 2 actually
 
Second section?
Ah, cool.
 
Yup, I finished chapter 1 yesterday
Alicia's last problem wasn't hard after all
It was only a hassle to understand what it actually said
 
@FernandoMartin Which one?
 
The last one from Alicia's exercise sheet
which is the last one from AM's chapter one as well
 
7:04 PM
The one about algebraic varieties
 
I have to finish those.
AGH!
 
I solved it and still don't understand it
 
HEHE
Tough life.
@FernandoMartin What definition of "Algebra over a ring $A$" do you use?
I haven't been able to find one.
 
An $A$-algebra $B$ is a ring and a ring morphism $A\rightarrow B$
thus $B$ inherits an $A$-module structure via the morphism
 
Oh, that's that?
 
7:10 PM
yup
 
Wait.
$A$ is any ring? Or commutative?
 
I think one works with commutative rings in this case
 
Did you notice that 2013 was the first year since 1987 that had 4 different digits ?
 
@GabrielR. LET ME WRITE THAT IN MY INVISIBLE TYPERWRITER OF INTERESTING FACTS.
 
2013 was also the first year since 2004 such that the sum of its digits is 6
@PedroTamaroff: stop objectifying women please
3
 
7:22 PM
@FernandoMartin Is this srs?
 
@FernandoMartin Hmm, not gonna read this now.
 
I didn't read the whole thing either. While what I said still makes sense for non-commutative $A$, you don't exactly get the same structure
 
7:46 PM
I tried to read some "non-commutative geometry" several years back. Hurt my brain.
 
was the problem with limit that was recently stated in the chat been solved?
I want to look at that simple solution. Anyway, I will never come up with it.
 
8:04 PM
 
oh, wait, I got the idea
 
Please, don't post animated GIFs in chat, it makes it hard to keep the window open and not be distracted by it.
 
Hi all! Here's a question about linear classification. If anyone has time to take a look, it would be great!
 
How can I express the Cartesian equation of a plane $\Pi$ in parametric form? Lets say I had $$ 2x - y + 3z = -6 $$
 
${\rm P = NP}$
0
Q: Complexity of general polynomial map evaluation is polynomial?

Enjoys MathA polynomial map is equal to another polynomial map iff they take on the same values at each point. So this is different from formal polynomials. So since in $\Bbb{Z}_p$, $x^{p-1} = 1$ for all $x \neq 0$, and is $0$ on $0$, we have that there are a finite number of polynomial maps in $\Bbb{Z}_...

 
8:21 PM
@ThomasAndrews Sorry; I'd delete it, but I only just noticed your message.
 
NP, just a guide. I used Adblock to hide that particular one. Lots of people do it - I find the inability to silence animated GIFs in Google+ infuriating.
 
adjoint functors <3
 
A generally good way to be treated like a crank is to jump onto a math chat room and suggest you have just solved P=NP in a one-page proof.
 
@ThomasAndrews CAN I HAZ LINK
Oh.
@EnjoysMath You so silly. =)
 
it is widely known that P=NP iff P=0 or N=1
 
8:28 PM
I learnt to play Rock (Iraq) Lobster today.
Today was a good day.
@FernandoMartin Do you like Satch?
Note the absence of an "n".
 
I used to
I saw him live back in 2008
 
I thought dividing by 0 wasn't well defined. Why does my book think otherwise? It says that my final equation for the line after being transformed by a 3x3 matrix is $$ \dfrac{x+6}{0} = \dfrac{y}{1} = \dfrac{z+12}{1} = \lambda $$
 
What's your book @Shisui?
 
@FernandoMartin cool
 
@FernandoMartin It's an Edexcel book for Further Maths.
I'll post the full question in a second
 
8:32 PM
@EnjoysMath I'd say the mistake is thinking the words "The pattern appears to be" is a rigorous statement.
 
@FernandoMartin I went to see him 2012 or 2013, with the G3.
 
@ALL, should I ask this question to MathSE, as well?
 
The transformation $ T : \mathbb{R}^{3} \to \mathbb{R}^3 $ is represented by the matrix $ \mathbf{\text{T}} $ where $$ \mathbf{\text{T}} = \begin{pmatrix} 2 & -1 & 3 \\ -1 & 4 & -2 \\ 3 & 2 & 4 \end{pmatrix} $$ The plane $ \Pi $ has equation $ 2x - y + 3z = -6 $. Show that the image of $\Pi$ under $T$ is a line and find Cartesian equations of this line.
@FernandoMartin
 
Happy Easter.
 
@Pedro: Vai/Satriani/?
 
8:41 PM
@FernandoMartin It was Petrucci, Satriani and the former lead guitar of Deep Purple.
 
@FernandoMartin What do you think of the question?
 
YAS.
It was around 4hs long.
 
I'd say $\frac{x+6}0$ is nonsensical
does the book say exactly that? maybe it's a typo
@Pedro: jeez
 
@ParthKohli Hi.
 
8:46 PM
Christmas Christmas time is here.
Oh, hey, I didn't see you guys all the way over here.
 
@FernandoMartin It does! It's driving me up the wall.
@FernandoMartin There's the full question and working.
 
That makes no sense
the equations are $x=6$, $y=z+12$
 
@FernandoMartin You're being trolled.
 
@PedroTamaroff Honestly, I'm not trolling @FernandoMartin.
 
Nah, it's just a shitty book
 
8:51 PM
The book is admittedly, terrible.
 
A good rule of thumb is: if a math book has colors in it, it sucks
I know no counterexample
 
@FernandoMartin Is there a way that you could combine both equations to make a final equation, or do you think it's sufficient to simply state those two above?
 
No, those two suffice
 
@FernandoMartin What do you mean?
 
another way to say that is that any point on that line is of the form $(6, z+12, z)$
 
8:53 PM
@PedroTamaroff le Klein quartic can be parameterized through 2-arg modular forms?
Who knew?
 
@Pedro: I don't know of any good math book that has colored boxes with annotations
 
@FernandoMartin Oh.
 
@FernandoMartin You mean $(6, y+12, z)$ right? I hardly ever use that book, but since my exam is based on most of its content, I thought I might give it a quick once over.
 
Well, Ted's book as some colors, but say because it has the picture of a goat over a sphere. =D
@BalarkaSen Known a long time ago.
 
No, I mean $(6,z+12,z)$ @Shisui
$y=z+12$
 
8:55 PM
@FernandoMartin Of course! My brain has been exhausted by this terrible book -_-
 
Sab
Hi all
 
@PedroTamaroff Borchardt is going off the top of my head.
=P
 
Sab
I'm new here and I have some questions.
 
@BalarkaSen Are you thinking of killing yourself?
Don't do it pal.
 
Sab
312
Q: Is this Batman equation for real?

a_hardinHardOCP has an image with an equation which apparently draws the Batman logo. Is this for real?

How do people make these stuff? I mean, what knowledge is required?
I saw a butterfly shape, lips and tongue shape etc.
 
8:57 PM
@Sab The Batman equation is highly nonamusing.
 
@PedroTamaroff Would make a mental note, thank you. By the way, I am learning hyperbolic geometry. Fun stuff.
 
Sab
@PedroTamaroff I'm fascinated by these stuff but I don't know how to make them. I certainly need to know the math but which part of math?
 
@Sab Read the answers.
They're very comprehensive.
 
Sab
It's too complex for me I'm 13
 
@Sab Just simple coordinate geometry.
 
8:59 PM
The math is stupi and uninteresting. Tou draw curves, essentially, piecewise.
@Sab Then wait.
 
Sab
I know differentiation, integration and some basic trigonometry and algebra.
Will these help?
 

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