\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
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\begin{document}
\begin{equation*}
   V_2(x) = \frac{1}{2} x_1^2 + \frac{1}{2}(x_2 + \frac{b}{c-a} x_1)^2
\end{equation*}
\end{document}