\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
\usepackage{color}
\pagestyle{empty}
\begin{document}
\begin{equation*}
\begin{aligned}
\dot x &=& Ax + Bu \\
y &=& Cx + Du
\end{aligned}
\end{equation*}
\end{document}