\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
\usepackage{color}
\pagestyle{empty}
\begin{document}
\begin{equation*}
  A = \begin{bmatrix} 0 & 1 \\ -\omega_0^2 & 0 \end{bmatrix},
\end{equation*}
\end{document}