$$\sqrt{a}-\sqrt{b}=\frac{a-b}{\sqrt{a}+\sqrt{b}}$$
$$\sum^{+\infty}_{n=1}{\frac{1}{n^2}}=\frac{\pi^2}{6}$$
$$\lim_{R \to +\infty}\int^{+R}_{-R}e^{-t^2}dt=\sqrt{\pi}$$
$$\forall{\epsilon>0}\space\space\exists{\delta}\ge0\space\space(|x-x_0| < \delta \implies |ln(x) - ln(x_0)|<\epsilon)$$
$$\sum^{+\infty}_{k=0}{\frac{1}{16^k}}(\frac{4}{8k+1}-\frac{2}{8k+4}-\frac{1}{/8k+5}-\frac{1}{8k-6})=\pi$$