
\documentclass{article}
\usepackage[body={8cm,8cm}]{geometry}
\usepackage{lmodern}
\usepackage{mathtools}
\pagestyle{empty}
\begin{document}
\[
{}^t
\begin{bmatrix}
   a & b \\  c & d \\
\end{bmatrix} 
=
\begin{bmatrix}
   a & c \\  b & d \\
\end{bmatrix}
\]
\end{document}
