\documentclass{article}

\documentclass{article}
\usepackage{amsmath} % pkg required by EasyLatex
\usepackage{amsfonts} % pkg required by EasyLatex
\usepackage{amssymb} % pkg required by EasyLatex
\usepackage{psfrag} % pkg required by EasyLatex
\usepackage[dvips]{graphicx} % pkg required by EasyLatex

\begin{document}

\begin{align*}
\left[ \begin{array}{lll}
a_{1,1} & a_{1,2} & a_{1,3}
\\ a_{2,1} & a_{2,2} & a_{2,3}
\\ a_{3,1} & a_{3,2} & a_{3,3}
\end{array} \right]
\end{align*}

\end{document}