# Babak S.

 42m comment If $d(x,A)=0\forall x\in X$ for some subset $A$ of $X$, does it follow that $A$ is dense?You mean $X$ and $A$ can not be disjoint? 47m comment $\int_{0}^{\pi/2} \text{arctanh}(\sin x) \text{arctan}(a \tan(x)) \cos(x) \ dx$Which problem led you to get this integral? 53m reviewed Approve suggested edit on similarity of triangles and tangents 1h reviewed Approve suggested edit on Find the limit without use of L'Hôpital or Taylor series: $\lim \limits_{x\rightarrow 0} \left(\frac{1}{x^2}-\frac{1}{\sin^2 x}\right)$ 1h reviewed Approve suggested edit on Find the limit without use of L'Hôpital or Taylor series: $\lim \limits_{x\rightarrow 0} \left(\frac{1}{x^2}-\frac{1}{\sin^2 x}\right)$ 1h comment How to solve $at + b = 0 \pmod {(a-t)}$?Nice Maisam. +1 1h comment Polynomial discrete mathematics+1 ${}{}{}{}{}$ 1h comment Commutator propertyMake it as an comment to @Don's leading answer, if you want him to have a looking at it. 1h comment Order 7 matrix with odd entries has determinant a multiple of 64?$3^i, i=2k$ mode $4$ 1h comment Cardinality of Center of p Groups $|Z(G)| \neq p^{n-1}$@MaisamHedyelloo: Thanks maiysam. Elthomas 2A. 1h comment Cardinality of Center of p Groups $|Z(G)| \neq p^{n-1}$@amWhy: I am glad cause of that. This is more precious to me that I can make someone around the World to have a good feeling. This shows that $0$ (it is me) is not nothing. :-) 1h comment $\lim_{x\to \pi/2} \;\frac 1{\sec x+ \tan x}$+1 nice and complete. 1h comment Why $\operatorname{rank}(A^* A)=\operatorname{rank}(A)$ is equivalent to $A^* Ax=0$ if and only if $Ax=0$?+1 and happy eid. Eltemase 2a. ;-) 1h reviewed Approve suggested edit on Proving a relation between $\sum\frac{1}{(2n-1)^2}$ and $\sum \frac{1}{n^2}$ 1h comment Divergence of $\sum_{n=2}^\infty\frac{1}{(\ln n)^x}$ for $x>1$@Gary: See this one math.stackexchange.com/a/398964/8581. :-) 1h comment Notation of Planes@amWhy: :-o ${}$ 11h revised Being inside or outside of an ellipseedited tags 11h comment Being inside or outside of an ellipse@Bedi: In fact on a line like $L$, $|OA|<|OP|$ which $P$ is the intersection of $L$ with ellipse. 11h reviewed Approve suggested edit on Show that $\alpha_1u+\alpha_2v+\alpha_3w=0\Rightarrow\alpha_1=\alpha_2=\alpha_3=0$ 11h answered Being inside or outside of an ellipse