\documentclass[12pt]{article}
\pagestyle{empty}
\begin{document}
\begin{displaymath}
p_{\rm trial}^{\rm arb}(r) = {{3}\over{r_{\rm high}^{3} - r_{\rm low}^{3}}} r^2
\end{displaymath}
\end{document}
\documentclass[12pt]{article}
\pagestyle{empty}
\begin{document}
\begin{displaymath}
p_{\rm trial}^{\rm arb}(r) = {{3}\over{r_{\rm high}^{3} - r_{\rm low}^{3}}} r^2
\end{displaymath}
\end{document}
::
::
::
