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\documentclass{article} \usepackage{amsmath} \usepackage{amssymb} \usepackage{amsfonts} \thispagestyle{empty} \begin{document} \begin{equation} y=\left\{ \begin{array}{cc} k_1(x-x_b)+y_b& x<x_b\\ k_2(x-x_b)+y_b& x\geq x_b \end{array} \right .\notag \end{equation} \end{document}