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\documentclass{article} \usepackage{amsmath} \usepackage{amssymb} \usepackage{amsfonts} \thispagestyle{empty} \begin{document} \begin{equation} P(x)=\left\{ \begin{array}{cc} \frac{1}{b-a}&a<x<b\\ 0&{\rm otherwise} \end{array} \right .\notag \end{equation} \end{document}