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4:01 PM
/me temps @DanielFischer with math.stackexchange.com/questions/1000606/…
@ZachSaucier I'll talk you through it, the question has a neat trick that if you spot yourself will be great, if I just do it, not so.
 
@DanielF How should "Bourbachique" be translated? "Bourbakist", perhaps?
 
@AlecTeal have a good way to graph it on PC?
online tool would be preferable
 
When simplifying expressions do u use $\iff$ or $=$ symbol, for example in $$(a + b)(a + b)/(a + b)(a - b) \iff (a + b)/(a - b)$$
 
@ZachSaucier don't graph it, get a pen and a bit of paper, start with $z=\sqrt{x^2+y^2}=r$ $z=r$ is really easy to sketch!
 
so I have to take a photo of the drawing then? XD
 
4:04 PM
Well $z=|r|$
 
I don't have a phone that takes good photos nor a camera
 
That means you can't post it, it doesn't mean you can't draw it.
 
@MikeMiller That would be the translation of Bourbakiste. I think the "chique" ending is related to "chic" and it's a play on words. Can we have context?
 
"Panorama des mathematiques pures: le choix bourbachique", a book by Dieudonne.
 
@MikeMiller Seems it isn't a word play, and just a softening of the k to get the ch. Still, it's about the choices of Bourbaki (the group), not of Bourbakists, so translating it as Bourbakist wouldn't be right. The choice of Bourbaki, or The Bourbakian choice, I'd think.
 
4:09 PM
@AlecTeal i.imgur.com/X5XESa0.png is my sketch based on what I'm picturing in my head
 
Fair. Thanks!
 
@ZachSaucier Ignore the x and y, the shape is a revolution, this just makes diagrams nasty.
 
@r9m Did I say that? I only remember you told me Lord Unreasonable ... ;)
@r9m Yeah, such a solution exists, of course, no need for using complex analysis at all (I didn't put on paper yet).
 
@AlecTeal "$x$ and $y$ act as coordinates on" some surface $S$ means that the restriction of the projection $(x,y,z) \mapsto (x,y)$ to $S$ is an bijection from $S$ to an open subset of $\mathbb{R}^2$ with continuous inverse (which then has the form $\Phi\colon (x,y) \mapsto (x,y,\varphi(x,y))$). Then $\Phi$ is a (global) parametrisation of the surface, and $\Phi^{-1}$ a coordinate chart. What you have to do is compute the Jacobian of $\Phi_\pi^{-1} \circ F \circ \Phi_A$.
 
@DanielFischer I can't view LaTeX can you post that as a comment (my bookmarks toolbar doesn't work and I also can't move tabs or drag links - I would restart firefox but there's a lot open ATM)
I'm not even joking, I wish I were.
 
4:21 PM
@AlecTeal I didn't spot any neat tricks
 
@ZachSaucier you should see that you have a segment of a circle, you literally just have to integrate from pi/4 to 0 with phi, or pi/4 to pi/2 depending on where phi=0 is, and theta from 0 to 2pi and p=0 to 6
What you have is actually a part of a sphere, if you were clever you could use work out what fraction you have and use volume for a sphere!
@ZachSaucier see it now?
@DanielFischer responded to comment,
 
So did I.
 
r9m
@Chris'ssis unreasonable at times no doubt :P but Lord Unreasonable none the less .. :P
 
@r9m :D
 
Thanks @DanielFischer
 
r9m
4:33 PM
@Chris'ssis okay ! :D please show me when you put things in paper :)
 
@r9m I just finished a proof that for sure will break many hearts ... :-)
 
r9m
@Chris'ssis heart break !! <(O_O)> omg ! meesa has a weak heart !!
 
@r9m OK
 
@r9m if you're older than or 17 years old watch Star Wars again
 
r9m
@AlecTeal why ?
 
4:36 PM
So you can appreciate how bad the prequels are
 
Seeing Jar Jar not get run down will upset you, and now you understand the story the character will make you wish Qui Gon had let natural selection take its course.
Haha @user130018 glad we agree, but also the first 3 were not safe from Lucas
 
@AlecTeal Main is read-only atm, so I post it here: The Jacobian depends on the used charts, but once you've chosen charts, you have "the" Jacobian in those coordinates. What is chart-independent is whether the Jacobian is $0$ [at a point on the surface] or not.
 
r9m
oh god .. I have seen it a long time ago ! I forgot almost everything in the movies !
@Chris'ssis what is the problem statement ?
 
@user130018 youtube.com/watch?v=PiDRgDmXGi4 I cringe now, I also hate the "look, the droids are slipping!" added, which also ruined Revenge of the Sith
@user130018 that vid is Jabba's palace, also weirdly before Lucas sold to Disney
 
:18434002$$ \int_0^1 \log^3\left(\frac{x}{2}+\sqrt{\frac{x^2}{4}+1}\right)\frac{dx}{x}$$
 
4:39 PM
@r9m seriously watch them again, until I did I couldn't see what was wrong with Jar Jar, now I have these weird fantasies involving Jar Jar, Gordan Freeman and the guy from "Will it blend" and Gordon brings a spare crowbar <3
@DanielFischer thanks, I thought this was the case, but I didn't have the confidence to be sure, thanks for your time, really!
Yeah...
@PedroTamaroff you were right, I am a very angry person
 
r9m
@Chris'ssis $\displaystyle \int_0^1 \log \left(\frac{x}{2}+\sqrt{\frac{x^2}{4}+1}\right)\frac{dx}{x} = \frac{3}{10}\zeta(2)$
I think this $log$ one (not the $log^3$) I have seen in M.Se too .. lemme check
 
@AlecTeal does you answer include the area above the inscribed cone?
in the image I'm talking about the kind of "ice cream" part of the ice cream cone ;)
 
@ZachSaucier do you know what a sphere is? Draw an isoc. triangle and get a ruler and put 0 at the apex, then sweep across, you'll find a triangle doesn't have constant distance from the apex to the opposite edge.
Then get a compass and draw part of a circle, you'll find the curve are points of equal distance from the centre.
 
5:05 PM
@r9m did you? OK
 
hmm site is offline
 
@Alizter?
 
@AlecTeal Yes
 
5:20 PM
Oh okay it is offline
 
For finding the volume bounded above by $z = 8-8\!\left(x^{2}+y^{2}\right)$ and below by $z = 4\!\left(x^{2}+y^{2}\right)^{2}-4$, I can break it up into find the volume from 0 to the top and then find the volume from the bottom to 0 (adding the two), correct?
 
@ZachSaucier seriously, if you have x^2+y^2 always think r^2
 
I know
and I did
I worked it out using r^2. I'm asking if my methodology is correct because I'm not getting the right answer
 
So if z=8(1-r^2) (upside down bucket) and the other is a bucket (like y=x^2 shape) in r we don't even have to think in three dimensions
Yes, adding it as two chunks is the right thing to do
One involves 4(r^2-1) and the other 8(1-r^2) I don't think the natural choice for where to split is zero though @ZachSaucier
 
isn't that where they meet?
r = 1, so z = 0?
 
5:26 PM
Or you could integrate along the bottom one till the top one
 
I tried both, still not getting it correct xD but thank you for checking my methodology
 
You're revolving, so I'd do the theta (where theta is an angle about the vertical axis) last because it'll be the easiest to do.
 
bah, Math.SE downtime / read-only mode?
 
yep
 
SE is down in general
 
5:28 PM
all sites^
are in "read only"
:(
 
@ZachSaucier and your question is the first one listed on the cite until the downtime is up, hah
 
So it's going to be the integral from 0 to 2pi of
the integral from 0 to (largest radius where they intersect)
the integral from 4(1-r^2) to 8(r^2-1) of 1
r dz dr d\theta @ZachSaucier
 
@AlecTeal the first is r^4
correct?
 
I dunno maybe, but it's an easy integral to do, the first one (the dz one) doesn't even have a z in the expression! So it's literally a subtraction
 
5:37 PM
123 testing
 
caught my problem: forgot the r in rdzdrdtheta
thanks @AlecTeal
still not getting the correct answer for the volume of cone/sphere though
I'll be back on later
bye for now guys, thanks for all the help
 
bye
and All Souls' Day if I don't see you tomorrow :-)
 
@ZachSaucier I just drew a picture!
 
yay Math.SE is back
 
6:09 PM
@Semiclassical You misspelled site as cite.
@alizter I am now thinking of getting the IB books instead. IB also offers math and further math.
 
@JasperLoy Up to uni I am sure everybody pretty much gets the same stuff
 
@Alizter Not really. The world is too big to say that. Hey if you want the IB books tell me, I found the perfect set. Only one such set exists now that covers everything.
My best friend has returned from Oxford. I will meet him on Mon.
 
Hi @JasperLoy
 
@user130018 Hello Bart.
I am happy that Ali and Bart are both here.
 
6:27 PM
@UserX That's a pity. It's a good problem.
@Nick I am the number terrorist.
@Mike You there? I have made some progress, methinks
@TedShifrin!
 
Hi @TedShifrin
 
Hmm, seems the new OS is having issues ... Howdy all.
 
Which OS
 
IOS on my iPad
 
i am thinking of a geometric way to realize $Gal(\bar{Q}/Q)$, @Ted
 
6:40 PM
Doubt it can be done :)
 
"thinking"
nothing wrong in thinking, right?
 
Not in George Orwell's 1984
 
@TedShifrin my line of thinking is that $\mathbf{Z}_p$ might have some connection with the inverse limit of $S^1$s with the covering maps $x \mapsto x^n$
thus analogizing this to arbitrary profinite groups
 
@BalarkaSen how would you solve it?
 
@UserX ok, wait what was the problem again?
 
6:48 PM
Let $n$ be a number that has exactly 4 divisors d1 d2 d3 d4 such that d1<d2<d3<d4 and d1+d2+d3+d4=640
 
which numbers have exactly four divisors, @UserX?
 
Find all possible $n$
That's the problem
 
@UserX think about it
 
Exactly 4 divisors would mean "4 primes" right?
 
no @Alec
n can be only product of two primes
 
6:49 PM
Dude I couldn't evaluate 2^59 mod 101 in less than an hour yesterday.
 
1, p, q, pq
 
Oooh right
Divisors!
Surely we have (wlog) 1<p<q<pq - so that's that bit sorted
 
so you just gotta solve 1 + p + q + pq = 640 with p > q
 
Then 1+p+q+pq=640 (I'm guessing you've done this already)
 
which is easily done
1 + p + q + pq = (1 + p)(1 + q) = 640.
 
6:51 PM
Well it doesn't matter that p>q @BalarkaSen, if this is not the case just swap 'em. What about equality BTW?
 
@AlecTeal p \neq q, i.e., n is squarefree
 
Right, also 60 or 640? I thought it was 640?
 
doesn't matter
the rest is pretty easy
 
No that was the easy bit, now it's hard!
 
just prime factorize 640 and check via brute force
 
6:52 PM
@BalarkaSen it's not quite true that $n$ can only be the product of two primes.
 
@MikeMiller eh?
 
well, it is, but there's a case you missed.
 
r9m
n can be p^3 as well
 
spoilers, @r9m :)
 
oh ah
but squarefree
:P
 
6:54 PM
problem never said squarefree
 
oh ok
1 < p < p^2 < p^3
 
Damn this has to be hard to brute force
Any easier way?
 
Hey just quickly, thanks guys, really. You've reminded me why I avoid number theory
 
@UserX it's not hard
 
@UserX it's not that hard, the answers are 589 and 553 :)
 
6:55 PM
$640 = 2^7 \cdot 5$
@Mike back to the inverse limit of S^1s.
 
@BalarkaSen wanna take a shot at the other NT problem too?
 
I have got some coherent results.
@UserX OK
oh noes @Mike is gone.
 
Let a parabola $y=x^2-(3a+5)x+186, a\in \Bbb R$. Find $a \in R$ such that the parabola crosses the x axis at points with integer coordinates
I got it in two ways, both stuck
 
@UserX you need solve y = x^2 - (3a + 5)x + 186 in integers, then?
that's a weird way of saying it.
oh wait
 
my internet is going up and down, @Balarka, but I'm too sick to do any thinking right now anyway
 
6:59 PM
we need to find a real a such that x^2 - (3a + 5)x + 186 = x has an integer solution
OK, @Mike. Get rest.
 
Vieta&quadratic formula, vieta couldn't get past the first step, quadratic I reached that the discriminant had to be a perfect square, and the numerator of the solution has to equal $2m$ for some $m \in \Bbb Z$
 
yeah you need to think about the disc
 
I'd love to, @Balarka
 
hi all
 
Why does WolframAlpha list the zero vector as an eigenvector
 
7:02 PM
@MikeMiller Well what's stopping you?
 
I just slept all night, it's hard to sleep again
 
And you are sick as in throwing up?
 
nah, just the flu
 
yikes
sorry to hear that. i just got up from one.
get the antibiotics and drinks lots of fluids
 
7:15 PM
did you get it from nick?
 
@Sawarnik?
 
@BalarkaSen doctor balarka.
@BalarkaSen he is having fever too..
 
thunks @Sawarnik
 
thunks?
 
thunks
 
7:22 PM
Don't get antibiotics for no reason
If your doctor hasn't prescribed them at least
You'll get your bacteria's plasmids new antibodies against medicine.
 
O_O such biology. much terms. so high-fi.
@Pedro Mike seriously got Ebola this time.
 
@BalarkaSen DAFAQ
 
Scroll above.
 
>>>>>>>>>>>>
 
<<<<<<<<<<<<<
 
7:36 PM
@BalarkaSen lol
@UserX Yes, obviously.
 
7:57 PM
Short of vote fraud, how can this have 7 upvotes and 6 favorites?
 
@DanielFischer Do you know this other classic : a function with Lipschitz constant $1$, over a compact and convex set has a fixed point ?
@justabrickinthewall would you run for moderator ?
 
Just found another instance of this sort.
 
Is fraud on MSE profitable or something
 
Fraud?
 
@G.T.R No, I would not. I am too active as a user / meta-user for that. A moderator should be more moderate.
 
8:04 PM
Okay I favourite stuff to mean "I should look at this later" and never do
But upvotes... okay
 
@justabrickinthewall in a few days, this data.stackexchange.com/math/query/edit/216040 will tell who favorited (if not sockpuppets)
 
@G.T.R Follows from this.
 
I am relieved to see that post #1000000 is not a homework dump, or "Hint: integrate by parts".
 
@justabrickinthewall who cares though?
Oh noes someone got 50 rep
I recently upvoted someone just so they could comment
 
They get 15 rep and can upvote other accounts. Those can upvote others. And so on. Six sock-puppets can mass-flag and delete anything.
 
8:09 PM
@justabrickinthewall If you look at the profiles of the askers, there is the curious coincidence that both (members for today) voted seven times, four times on questions, and three times on answers. Hmmm.
 
The filters will catch that surely?
math.stackexchange.com/questions/1001423/… mmm unanswered question with no votes or favs.... but honestly what does it matter? Preventing someone getting 6 accounts so they can delete stuff seems... a lot of work for a rare event
 
Okay @DanielFischer that is weird.
I wish they wouldn't allow user[whatever], makes it hard to tell them apart.
 
A voting ring is good for more than just mass-flagging. If left uncaught, they expand and become more difficult to clean out. More common on SO than here, so far.
 
Yeah SO is really bad, even for cliches
@justabrickinthewall math.stackexchange.com/questions/849463/… 9 upvotes
 
r9m
8:22 PM
@justabrickinthewall are you the author of mathindex.wordpress.com ? Its really useful ! Nice !!! .. I just found nice links to a bunch of series I was looking for !! :-)
 
That one is probably not fraud, but an indication of the site's voting standards.
 
Right. It makes sense, even if it's a poor question.
 
@r9m Thanks! (In this context, I have to say that r9m is not a sockpuppet account that I planted to promote the site. :)
 
r9m
:P lol haha
 
8:24 PM
@justabrickinthewall I hate it, someone puts a homework question and people always answer before me. I post a question and because it's not easy stuff any more - no one answers.
 
@justabrickinthewall Unrelated, what had the smoke detector against the user name "baba ji"?
 
@DanielFischer where's Robjohn?
 
@DanielFischer Baba Ji is one of most famous spammers on SE. Vashikaran Specialist, black magic, and so on. So they added the name to the watch list.
 
Black magic...lol
 
@justabrickinthewall I live a sheltered life ;)
 
8:27 PM
Yes, that. Now when this user posts somewhere on SE, detector raises alarm.
This is how I saw one of his questions, and answered it. :)
 
@AlecTeal Somewhere in California, I believe.
 
@justabrickinthewall Can't see askubuntu deleted posts :(
 
Me neither, but you see the post title in URL. There is not much to add to that.
 
Troo.
 
8:32 PM
@AlecTeal Your question about covering map is difficult to approach, because it's not clear what you know (open mapping theorem in complex analysis), and what you need (exactly what is your definition of covering map)?
The idea of writing $\mathbb C$ as the product of half-line with circle is good.
But attaching special significance to $\theta=0$ works against you. Instead, you could observe that the angle-doubling map can be inverted on any proper subarc, etc.
 
@justabrickinthewall covering map is a topological thing, also I need to give $\theta=0$ attention (which is easy enough) because then I can have a neigh. around a complex point of argument 0.
 
@r9m I know :P
 
@justabrickinthewall I'm not being condescending or anything but this is the definition of a covering map
 
@r9m You were talking once about candies, but I never gave you my opinion about sos's questions. I think they are all candies too. I and sos think the same about our questions. :-)
hmmm, I'm annoyed that no one has come up with another solution to this candy
8
Q: An integral by O. Furdui $\int_0^1 \log^2(\sqrt{1+x}-\sqrt{1-x}) \ dx$

Chris's sisThe following integral was proposed in a paper by O. Furdui, namely $$\int_0^1 \log^2(\sqrt{1+x}-\sqrt{1-x}) \ dx$$ and then the generalization $$\int_0^1 \log^2(\sqrt[k]{1+x}-\sqrt[k]{1-x}) \ dx$$ As regards the first integral, my approach was to combine the integration by parts and the va...

I would have liked to learn a totally different way (or more ways, of course) ...
 
r9m
8:45 PM
@Chris'ssis Willie Wonka and his Chocolate factory ... sequel : Chris'ssister in candy land :P
 
@r9m Just saying ... no harm ... ;)
@r9m The real challenges are represented by questions like this one $$\sum_{n=1}^{\infty} (-1)^{n+1} \frac{H_n \log(n)}{n}$$
 
r9m
sigh .. that guy does not talk to me anymore .. must be upset about something I said/did :( ..
 
@r9m ^^^
 
r9m
@Chris'ssis does that have a closed form ? I am really clueless ..
 
@r9m $$\LARGE \text{WHO KNOWS? :-)}$$
 
r9m
8:50 PM
@Chris'ssis oh btw I added your+winther's solutions in my blog :-) that makes an excellent proof of the limit #(53) in wolfram catalan constant page :)
@Chris'ssis that is the real question ! ;)
 
@r9m Good. What is your blog now? You periodically change its name.
 
@r9m that one is a limit I love!
 
r9m
@Chris'ssis :D fabulous result !!!
 
:1843586 It seems that approach was unknown, and it's not hard.
 
r9m
8:55 PM
@Chris'ssis cool !!
 
@r9m Hehe, winther was a bit surprised by the connection I did. Read our comments. :D
 
r9m
@Chris'ssis yes I read them !! :D
 
@alizter Wow, I just found out all about IB math. It seems that taking IB Math HL and IB Further Math HL is about the same as taking A Level Math and A Level Further Math.
@user130018 What are you doing right now?
 
9:30 PM
@r9m Have you seen this one by Furdui?
$$\int_0^{\infty} \int_0^{\infty} \frac{\sin(\alpha x) \sin(\beta y)}{x y (x+y)} \ dx \ dy$$
 
r9m
@Chris'ssis nope .. seeing it for the first time
 
9:45 PM
@Balarka: You're supposed to be asleep.
 
@TedShifrin How would our world look like without integrals, series and limits?
 
@TedShifrin I am supposed to be and supposed to do many things I am not and not doing.
Respectively.
 
or was that respectfully?
Probably just fine, @Chris'ssis. There is no need for obsession.
 
I am obsessed with number theory, @Ted
Obsessively obsessed.
 
Well, I'm not fond of any obsession.
As I've made clear before. I prefer balance in life, balance in mathematics.
 
9:47 PM
@Chris'ssis if ints, series and lims were forgotten by everyone today, tommorow there would be 10 research papers re-inventing them
2
 
@TedShifrin Ugh.
 
r9m
@UserX TRUTH !!!!! :D
 
You don't have to like me, @Balarka or @Chris'ssis.
 
@UserX Very well said!
 
Join René :P
 
9:48 PM
:P
No thanks.
 
You can still dislike me without joining that nut.
 
I never said I dislike you.
 
r9m
Who is Rene ?
 
You are in fact one of the guys who inspire me.
 
I doubt that, @Balarka, but thanks.
 
9:49 PM
@TedShifrin Then we say, "R.I.P., modern technology"
 
@r9m Someone you should not know.
 
to some extent, @Chris'ssis ... but I stand by my desire for breadth and not absurd obsession.
 
r9m
@BalarkaSen :P lol
 
My point is you can't say "if there were no series, ints and lims" because they would be reinvtented soon enough
 
it's hard to recapture the 18th and 19th centuries instantaneously, @UserX
 
9:51 PM
@TedShifrin Well I would sure consider it a great achievement to EVER become a mathematician like you. I do respect mathematical intellect, regardless of branches of mathematics on which it is used on.
 
@TedShifrin It is, with our current knowledge of higher maths it wouldn't take more than a day to reinvent them I guess
 
@Balarka: Although I've published some nice research, I think you should aspire to far greater.
 
You'd soon stand corrected.
 
Well, @UserX, that's sort of silly. Our current knowledge incorporates all those centuries of work.
 
We're not saying "if everything from calc1 and higher was forgotten"
 
r9m
9:52 PM
@BalarkaSen is it Rene Schipperus ? :P lol (he answers Geometry questions too)
 
If we forget a part of it we would reinvent it almost instantly
 
that's the problem, @r9m ... He answers everything, whether he knows how to do it correctly or not. Some things he does very nicely.
 
@TedShifrin It's not obsession, it's simply too much stuff around, there are tons of integrals, series and limits, and it's more than that, one needs years to bring the knowledge to the art level and nicely compute them.
 
He got an RH.
 
But he detests me, @r9m and has made numerous ad hominem attacks.
it's just not that interesting to most of us, @Chris'ssis ... so don't expect it to be.
 
9:54 PM
@BalarkaSen isn't RH the riemann hypothesis?
 
no, it is the reputation hysteria
 
LOL @Balarka
yes, you are quite right
 
Is euclidean geometry a proof based class if taught right?
 
classically, yes, @UserX ... these days, not so much ... in the US, anyhow
 
@TedShifrin I can agree with that, sure, it's a matter of taste too, but I'm trying to point out that it's not about an obsession, it's a huge amount of stuff around.
 
9:56 PM
but not all stuff is equally important
 
@TedShifrin astrology vs math
My counter-example
 
counterexample to what, @UserX?
 
r9m
@TedShifrin attacks ?! that's not an acceptable behavior in a community :| (although I have seen lots of great (great answerers) users leave behind attacking comments)
 
Read your sentence as "but all stuff is equally important"
 
"not all stuff are equally important", I presume, @Ted
 
9:57 PM
the syntax is wrong in yours, @Balarka ...
 
So no counter example
 
No, @UserX. Astrology is as important as math.
 
needs another martini
 
LOL
 
@BalarkaSen elaborate
 
9:58 PM
@TedShifrin This is terribly hard to say since integrals, series and limits are critical in many fields. Who can say what is important and what not?
 
You can define a scale of importancy, it won't be objective though
 
@UserX astrology --> astronomy. it is the root of astronomy.
 
Of course they are, @Chris'ssis ... but your litany of obscure ones is not.
2
 
i'd rather fight with you to convince you that all of science is as important as math.
 

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