\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
\usepackage{color}
\pagestyle{empty}
\begin{document}
\begin{equation*}
  y(t)=\frac{1}{\tau}\int_{t-\tau}^tu(v)dv,
\end{equation*}
\end{document}