\documentclass[]{slides}
\usepackage{epsfig,colordvi,color}

\begin{document}
% Subscript style
\newcommand{\subs}[1]{\mathrm{#1}}
\begin{center}
$\frac{1}{z + 1 - C_2 z^{-1} - C_3 z^{-2}}$
\end{center}
\end{document}
