\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
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\begin{document}
\begin{equation*}
  \frac{dz}{dt} =
  \begin{bmatrix} z_4 \\ z_5 \\ z_6 \\
    -g \sin z_3 - \frac{c}{m} \, z_4 \\
    g (\cos z_3 - 1) - \frac{c}{m} \, z_5 \\
    0
  \end{bmatrix},
\end{equation*}
\end{document}