\documentclass[12pt]{article} \pagestyle{empty} \begin{document} \begin{displaymath} p_{\rm trial}^{\rm ideal,discrete}(r) = {{r^2}\over{\sum_{i=1}^{n_{\rm finite}} r_i^2}} \end{displaymath} \end{document}
\documentclass[12pt]{article} \pagestyle{empty} \begin{document} \begin{displaymath} p_{\rm trial}^{\rm ideal,discrete}(r) = {{r^2}\over{\sum_{i=1}^{n_{\rm finite}} r_i^2}} \end{displaymath} \end{document}