\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
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\begin{document}
\begin{equation*}
  \tilde M(q) \ddot x + \tilde C(q, \dot q) \dot x + \tilde N(q, \dot
  q) = F,
\end{equation*}
\end{document}