\documentclass[12pt]{article}
\thispagestyle{empty}
\usepackage{amsmath}
\begin{document}
\huge{
$I = |A|^2 + |B|^2 + |A| |B| \exp(i (\theta - \phi)) + |A| |B| \exp(-i (\theta - \phi))$
}
\end{document}
