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An expert is a man who has made all the mistakes, which can be made, in a very narrow field. (Niels Bohr)


Apr
20
comment What should one do if one works on a problem and submits a paper only to find that it is already in some book?
@MathAM You could paper to write a review if the path you took if your work is essentially different from the work done in the book.
Apr
19
comment Proving $\int_{0}^{\infty} \mathrm{e}^{-x^2} dx = \dfrac{\sqrt \pi}{2}$
Yocks. This method exploits the asymptotic behavior of exponential functions in a surprising way!
Apr
5
comment showing $Q[\sqrt 2] = Q(\sqrt 2)$
Hi Joe. Forgive my possible ignorance. But the statement " Before all is clear que $ \mathbb{Q}[\sqrt{2}] \subseteq \mathbb{Q}(\sqrt{2})$ " is not at all clear.
Mar
21
comment Prove that $\mu(a, b)= \mu(1, b/a)$.
Also add the reference (and the relevant page) this exercise. That way, members of the MSE help you.
Mar
11
comment Inexact Newton method.
@LutzL I know the Newton-Kantorovich theorem and its several versions. The point is that this question calls for a robust version of the Kantorovich theorem. And not only robust robust locally but globally robust.
Feb
4
comment Growth Rate. A precise definition.
OK. Recently I realized that his point of view refers to something we can call "discrete derivative". Could you explain your point of view? An example? I thank you.
Jan
28
comment Suppose G has order 4, but contains no element of order 4. A) prove that no element of G has order 3.?
This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient reputation you will be able to comment on any post.
Jan
25
comment how to find $ \lim\limits_{x \to \infty} \left(\sqrt{x^2 +1} +\sqrt{4x^2 + 1} - \sqrt{9x^2 + 1}\right)$
Very nice this trick!
Jan
14
comment Proof that $x^k < k^x$
@Setzer22 yes, $\log_{\,k} k=1$.
Jan
7
comment Growth Rate. A precise definition.
Thanks and +1. After a while I discovered that the answer given by the source of this problem is 20.050 copies
Dec
29
comment Dirichlet Problem on the unit disk
Welcome to Math StackExchange. Please be more clear in your question. Define C-harmonic function.
Dec
28
comment properties of positive definite matrix
@user115927, I use in my answer the fact that $Av=\lambda\cdot v\Leftrightarrow v^T(Av)=v^T(\lambda\cdot v)=\lambda\|v\|^2$. Then, $\lambda\geq 0\Leftrightarrow v^T(Av)\geq 0$.
Dec
24
comment The problem of the most visited point.
@GitGud This is the classic solution to the problem of the most visited point. In this case I would have to calculate the number of two distinct paths connecting two points. It seems to be a promising approach. But I have not had progress with this approach.
Nov
16
comment For what values will f(x) be necessarily one-one?
possible duplicate of How to prove that f is one-to-one
Nov
16
comment Equicontinuity and Uniform Boundedness
@Tom I think that the result might be right if $f$ is constant on the boundary of $U$.
Nov
16
comment Equicontinuity and Uniform Boundedness
@John Would not need the compactness of the $U$?
Nov
13
comment Find the limit of $\lim_{x\to\infty}\frac{\sin[xf(x)]}{x\cdot\sin[f(x)]}$
I think you should add the hypothesis that $\lim_{x\to \infty}x\cdot f(x)=0$. Use the Limit Theorem for Composite Functions: $\lim_{u\to \infty}h(u)=M$ and $\lim_{x\to a}u(x)=L$ implies $\lim_{x\to a}h(u(x))=M$
Nov
12
comment Equivalence of intrinsic and extrinsic metrics of embedded manifolds.
As you can clearly see that small $d_{\mathcal{M}}$ implies $d_{}$ small?
Nov
12
comment Frobenius Norm with Unitary Operators
@user108149 Now I think my answer clearer for you enteder. I have helped.
Oct
30
comment Percolation and number of phases in the 2D Ising model.
See question too on physics.stackexchange.com/questions/81903/…