\documentclass[preview,border=12pt,varwidth]{standalone}% change it back to your own document class
\usepackage{amsmath}
\begin{document}
\abovedisplayskip=0pt\relax% remove this line in your production
\begin{gather*}
\int \sec^2(5 - 3x/4)\,\mathrm{d}x\\
\int \frac{1}{\cos^2 (5 - 3x/4)}\,\mathrm{d}x
\end{gather*}
\end{document}

How to remove the white space on the left of gather* when using standalone class?

$\begin{gathered}...\end{gathered}$– egreg Nov 24 '13 at 13:46