@BalarkaSen still trying to cheat a little. The transition matrix between the standard basis to the spherical frame should (I think) have orthogonal columns since the latter is an orthogonal basis. This transition matrix is the Jacobian at a given point, so doesn't this prove the orthogonality of the columns?
if you're nervous readers might misunderstand, you can briefly remark your notation to clarify $[A\subseteq B]\Longleftrightarrow [(A\subsetneq B)\lor (A=B)]$
@Arrow I don't understand what you're trying to do. I mean, just computing the Jacobian shows they have orthogonal columns and you can do it on your head.
$$\dfrac{4^{n+1}}{n+2}<\dfrac{(2n)!}{(n!)^2}\cdot\dfrac{4(n+1)}{n+2}=\dfrac{(2n+2)!}{((n+1)!)^2}\cdot\underbrace{\dfrac{4(n+1)^3}{(n+2)(2n+1)(2n+2)}}_{\text{less than } 1}<\dfrac{(2n+2)!}{((n+1)!)^2}$$
The quotient is less than 1. You can check that the difference in the polynomials is positive for $n>1$ @saturatedexpo
I personally feel dealing with this problems with fractions is a lot of hard work for little benefit. It's much more natural to show that $4^n (n!)^2 \lt (2n)!(n+1)$
@Brody I'm going to give you some homework for the next time we talk : learn and understand cross product and it's geometric meaning from chapter 1, section 5. Then we can talk about volume of surfaces and it's relation with Riemannian metrics.
Sure, time isn't a factor. Also, chapter 3 section 5 contains a proof of equivalence of the two definitions of arclength. I think you'd be able to understand it just fine.
Feel free to not bother with any of these if you don't care though! I am just giving you "homeworks" to get you started and put something in the back of the mind as a motivation.
I feel like my brain continually atrophies without proper stimulation, so that's all welcomed. I'm also very endeared by your care and effort to spur another's growth in math
@Brody Yes, mine does that too. I think multivariable calculus, with appropriate care, can be very interesting 'cause it's the gateway drug to lots and lots of interesting mathematics. Ted does that a lot throughout the book, but since you already know some of the multivariable calc (although in a not very motivated way, as I gather), I think I can tell you a bit more.
And sure, I like to talk math with people who like math.
@BalarkaSen suppose I wish mathematics were more complete in general. We have solid theorems and understanding of various algebras, various variables and dimensions, various hyper-operations, altogether working
it is already pretty big, to the point where we got statements that are true but cant be proven. So what is exactly your wish? That all subfields of Math work together?
i mean that taking a course in set theory makes you pretty much ready for everything?
@BalarkaSen Actually, there's some leisure in looking at the established repertoire and marveling at the objects and relationships we already understand. But that's just one aspect of the job
@saturatedexpo Think of sailing a ship to the New World. You have the shoreline in mind, but miles and miles of harsh sea life before you ever might reach it (like working an unsolved problem)
@BalarkaSen I know. But I personally do seriously consider certain paths just for the money, even if to the potential diminution of learning rich, beautiful math
Let $C\subset\Bbb R$ be the smallest set containing $0$ and closed under whole number addition/subtraction, whole number exponents, and whole number roots. That is, for all $c\in C$ and $n\in\Bbb N$, we have $c\pm n\in C$, $c^n\in C$, and $c^{1/n}\in C$.
We know that $\sqrt2+\sqrt3\in C$, since ...
When solving different equations, I have realised, that some roots containing only arithmetic operations and square roots (4th, 8th roots too, because they can be represented using only square roots) can be converted to nested square roots form. Examples (these are roots of equations of 2nd, 4th,...
I was playing around with factorials the other day, and I realized that $4!+5!$ is a perfect square. Perplexed by this result, I started looking for other pairs of factorials that produce a perfect square when added together (unbeknownst to me, I had stumbled across a well-known open problem in n...
i doubt anyone would want to do anything unless you choose a really wrong answer and even then probably people wont care but it brings the question back to the active list
When would it be reasonable to start a bounty on an unanswered question? I asked this question a week and a half ago, and it still has no answer. I've been stuck on the problem for months, but I'm thinking I should wait another month or two to start a bounty
Inspired by this question and this answer, I decided to investigate the family of integrals $$I(k)=\int_0^e\mathrm{Li}_k(\ln{x})\,dx,\tag{1}$$
where $\mathrm{Li}_k(z)$ represents the polylogarithm of order $k$ and argument $z$. $I(1)$ evaluates to $e\gamma$, but $I(2)$ has resisted my efforts (wh...