\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath}
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\begin{document}
\begin{equation*} 
V_\text{ext}(\mathbf{r})=\frac{1}{2}m \omega^2 |\mathbf{r}|^2
\end{equation*}
\end{document}