\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
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\begin{document}
\begin{equation*}
 \int_{t_1}^{t_2} \Bigl|V_{in}(t)-
  V_{out}(t)\Bigr|dt\leq a,
\end{equation*}
\end{document}