Jack D'Aurizio
Reputation
121,260
96/100 score
 12h revised Straight Edge - Only Geometric Construction added 90 characters in body 12h answered Straight Edge - Only Geometric Construction 13h comment An integral related with the Riemann $\zeta$ function @Dr.MV: that is a nice shortcut, thank you, Mark. 13h revised Is $\sum\limits_{n=1}^\infty \frac{|\sin n|^n}n$ convergent？ added 34 characters in body 13h revised An integral related with the Riemann $\zeta$ function deleted 4 characters in body 13h revised An integral related with the Riemann $\zeta$ function edited tags; edited title 13h answered An integral related with the Riemann $\zeta$ function 15h reviewed Edit Prove that $\tan20^\circ\tan40^\circ\tan60^\circ\tan80^\circ=3$ 15h revised Prove that $\tan20^\circ\tan40^\circ\tan60^\circ\tan80^\circ=3$ I changed 60^{0} into 60^{\circ} to eliminate possible confusion. 16h answered Determine wether $\sum_{n=1}^\infty \frac{3n-1}{(n+1)^3}$ converges or diverges. 16h answered Is there closed form of integral of gamma function with specific range 1d accepted A nice and hard colouring problem 1d awarded Nice Answer 1d awarded Nice Answer 2d awarded Nice Answer 2d comment Tridiagonal band matrix, finding its inverse norm See identity $(19)$ here: mathworld.wolfram.com/ChebyshevPolynomialoftheSecondKind.html. The eigenvalues of your matrix are not difficult to find. 2d comment Is $f(x)=\sum_{n\geq 1}\frac{(-x)^n}{n^2+1}$ convex at $x=0$? It is a convex function for every $x\in(-1,1)$. 2d revised Is $f(x)=\sum_{n\geq 1}\frac{(-x)^n}{n^2+1}$ convex at $x=0$? added 295 characters in body 2d comment Is $f(x)=\sum_{n\geq 1}\frac{(-x)^n}{n^2+1}$ convex at $x=0$? We may say even more than convexity holds in a neighbourhood of zero. Such a function is convex on the whole interval of convergence $[-1,1]$. 2d revised Is $f(x)=\sum_{n\geq 1}\frac{(-x)^n}{n^2+1}$ convex at $x=0$? edited title