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:

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

The & sign separates columns and the "\\" separates the rowsBold text

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