\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
\usepackage{color}
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\begin{document}
\begin{equation*}
  \aligned 
    \frac{d}{dt}\bmatrix p \\ \theta \\ \dot p \\ \dot \theta \endbmatrix &=
    {\bmatrix
      0 & 0 & 1 & 0 \\
      0 & 0 & 0 & 1 \\[1ex]
      0 & \frac{m^2 l^2 g}{\mu}
        & \frac{-c J_t}{\mu} 
	& \underline{\frac{-\gamma J_t l m}{\mu}} \\[2ex]
      0 & \frac{M_t m g l}{\mu}
        & \underline{\frac{-c l m}{\mu}}
        & \underline{\frac{-\gamma M_t}{\mu}}
    \endbmatrix} \bmatrix p \\ \theta \\ \dot p \\ \dot \theta \endbmatrix + 
    {\bmatrix
      0 \\ 0 \\[1ex]
        \frac{J_t}{\mu} \\[2ex] 
        \frac{l m}{\mu} 
    \endbmatrix} u \\[1ex]
    y &= \bmatrix 1 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 \endbmatrix x,
  \endaligned
\end{equation*}
\end{document}