Matrix equations are not working

Matrix equations are working in html page, but its not working in mpdf after submitting a form.

Example code :
<p>\[ \left( \begin{array}{cc}
1 & 0 \\
0 & 1
\end{array} \right)
%
\left( \begin{array}{cc}
1 & 0 \\
0 & 1
\end{array} \right)
\]</p>