\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
\usepackage{color}
\pagestyle{empty}
\begin{document}
\begin{equation*}
  P(s) = H_i(0) P_o(s) = \frac{H_i(0)}{m s^2 + c s},
\end{equation*}
\end{document}