\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
\usepackage{color}
\pagestyle{empty}
\begin{document}
\begin{equation*}
\frac{d}{dt} \begin{bmatrix} z_1 \\ z_2 \end{bmatrix} = \cdots
\end{equation*}
\end{document}