\documentclass[12pt]{article}
\usepackage{amssymb,amsmath}
\pagestyle{empty}
\begin{document}
% Beispiel von Grätzer, George A.
% Math into LaTeX : an introduction to LaTeX and AMS-LaTeX
% Birkhäuser Boston 1996 entnommen
\begin{align}
m &= \frac{m_0}{\sqrt{1-\frac{v^2}{c^2}}} \\
ds^2 &= c^2dt^2-dx^2-dy^2-dz^2
\end{align}
\end{document}