\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
\usepackage{color}
\pagestyle{empty}
\begin{document}
\begin{equation*}
  e^{(\sigma+j\omega)t} = e^{\sigma t} e^{j\omega t} = 
  e^{\sigma t} (\cos{\omega t} + j\sin{\omega t}),
\end{equation*}
\end{document}