Math Formula on Wiki

Use this website for formula $\operatorname {erfc} (x)={\frac {2}{\sqrt {\pi }}}\int _{x}^{\infty }e^{-t^{2}}\,dt={\frac {e^{-x^{2}}}{x{\sqrt {\pi }}}}\sum _{n=0}^{\infty }(-1)^{n}{\frac {(2n)!}{n!(2x)^{2n}}}$

${\pi }={\frac {3}{4}}{\sqrt {3}}+24{\int _{0}^{1/4}}{{\sqrt {x-x^{2}}}dx}$

${\sqrt {3x-1}}+(1+x)^{2}$

${\pi }r^{2}$ $4{\pi }{\epsilon }r^{2}$

How to write a matrix:

<math> \begin{matrix} a & b \\ d & e \end{matrix}</math>

${\begin{matrix}a&b\\d&e\end{matrix}}$