\documentclass[12pt]{article}
\thispagestyle{empty}
\usepackage{amsmath}
\begin{document}
\huge{
$\psi( \vec{r},t) = \psi_0 \exp\left(\frac{i}{\hbar}\left( \vec{p}\cdot\vec{r} - E t \right) \right)$
}
\end{document}
