\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
\usepackage{color}
\pagestyle{empty}
\begin{document}
\begin{equation*}
  P(s) = \frac{a(s)}{b(s)} = \frac{A(s)}{B(s)},
\end{equation*}
\end{document}