
\documentclass{article}
\usepackage[body={8cm,8cm}]{geometry}
\usepackage{lmodern}
\usepackage{mathtools}
\pagestyle{empty}
\begin{document}
Voici un exemple~:
\begin{align}
   x + 4 & =  0 \notag \\
   8 - y & =  0. 
\end{align}
\end{document}
