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 Nov16 comment How to find $x$ such that $\tan5x=\tan x$ and $\sin5x=\sin x$? You are welcome :) Nov16 revised How to find $x$ such that $\tan5x=\tan x$ and $\sin5x=\sin x$? sin to \sin, x to $x$ Nov16 suggested approved edit on How to find $x$ such that $\tan5x=\tan x$ and $\sin5x=\sin x$? Nov16 revised How can I solve this infinite sum? deleted 2 characters in body Nov15 answered When will $AB=BA$? Sep24 awarded Autobiographer Aug12 comment What is the oldest open problem in geometry? I would like to see an animation for a periodic orbit in an obtuse triangle. Jul24 revised Probability with Uniform Distribution with Multiple Variables texified the body Jul24 suggested approved edit on Probability with Uniform Distribution with Multiple Variables Jul11 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. Jul4 comment 'Obvious' theorems that are actually false You may be interested in these books: Counterexamples in Analysis, Counterexamples in Topology, and Counterexamples in Probability. Jul2 comment How to prove that: $\tan(3\pi/11) + 4\sin(2\pi/11) = \sqrt{11}$ How did you reach the $\sum_i \omega^{2i}=0$? Jul2 awarded Curious Jun19 revised Find an invertible matrix $P$ and a diagonal matrix $D$ such that $D=P^{−1}AP$? Texify the title Jun19 suggested approved edit on Find an invertible matrix $P$ and a diagonal matrix $D$ such that $D=P^{−1}AP$? Jun19 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 $\int u^{-1}f(u)\,\mathrm{d}u$. Jun19 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 $\alpha_5=0$. May17 awarded Yearling Apr20 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? Apr19 asked Givens rotation and retraction mapping