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visits member for 3 years, 7 months
seen Dec 16 at 12:29

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Nov
16
comment How to find $x$ such that $\tan5x=\tan x$ and $\sin5x=\sin x$?
You are welcome :)
Aug
12
comment What is the oldest open problem in geometry?
I would like to see an animation for a periodic orbit in an obtuse triangle.
Jul
11
comment Limit of the integral: $\int_0^{\pi/2}\beta^\alpha\exp\left(-\beta\cos(\theta)\right)d\theta$
Shouldn't it be $\lim_{\beta\to+\infty}J_0(\beta)=0$? Illustration.
Jul
4
comment 'Obvious' theorems that are actually false
You may be interested in these books: Counterexamples in Analysis, Counterexamples in Topology, and Counterexamples in Probability.
Jul
2
comment How to prove that: $\tan(3\pi/11) + 4\sin(2\pi/11) = \sqrt{11}$
How did you reach the $\sum_i \omega^{2i}=0$?
Jun
19
comment How to evaluate the following integral? $\int \ln(e^x + c)~\mathrm dx$
When faced with $\int f(e^x)\,\mathrm{d}x$, try transform it into $\int u^{-1}f(u)\,\mathrm{d}u$.
Jun
19
comment Clarification on optimization problem
I think for any $\alpha_k$, the objective function is linear. Given that the constraint is also linear, the optimum lies in some corner point. Since $\alpha_5=1$ violates the constraint, so $\alpha_5=0$.
Apr
20
comment Givens rotation and retraction mapping
Thanks. I am fine with the QR/polar decomposition and exponential mapping, but I am not clear about the part of Givens rotation in the text. Also, any references for the "closest" property of polar decomposition?
Feb
18
comment Homework problem on continuity
I think differentiability implies continuity.
Jan
23
comment $QQ$-plot - Why do we choose the empirical distribution $F_n(x) = \frac {\#\{y \in S \mid y \le x\}} n$, $S$ is sample, for comparison with normal?
Just to mention that there is another SE site for statistics: stats.stackexchange.com
Jan
23
comment Correspondence between an order of rational function field and a Dedekind cut
Thanks. Then where does the $a$ come from? It seems to me that $X>_{\mathbb{R}(x)}x\iff X-x>_{\mathbb{R}(x)}0\iff -x >_\mathbb{R}0 \iff x<_\mathbb{R} 0$.
Jan
8
comment How prove this inequality $(a^2+bc^4)(b^2+ca^4)(c^2+ab^4) \leq 64$
Maybe different patterns of lines, if that's convenient for you.
Jan
8
comment Set of critical points of polynomial: why finite
When you say a polynomial defined on $\mathbb{R}^n$, does it mean a multivariate polynomial with $n$ variables?
Jan
8
comment How prove this inequality $(a^2+bc^4)(b^2+ca^4)(c^2+ab^4) \leq 64$
Can you use other colors? Since many people have protanopia or protanomaly (like me).
Jan
4
comment KullbackÔÇôLeibler divergence with elements that are $0$
How about additive smoothing?
Dec
16
comment Find derivative of $f(x)=(x+2)^{(x-1)}$
OK, I get it. It has nothing to do with the logarithm.
Dec
16
comment Find derivative of $f(x)=(x+2)^{(x-1)}$
Sounds like the same as $f$ except for the positiveness.
Dec
16
comment Find derivative of $f(x)=(x+2)^{(x-1)}$
What are $a$, $b$ and $c$ here?
Nov
12
comment solution of $y^2 - x = 15$ and $x^2 -xy = 2009$
What do you mean by the symbol "|".
Nov
12
comment Infinite self-convolution for a function
Convolution corresponds to the PDF of the sum of random variables. I think something can be obtained by the law of large numbers.