\documentclass[a4paper,12pt]{article}
\newcommand\ds{\displaystyle}
\begin{document}

\parindent=0pt

QUESTION

Given that
$\textbf{C}=\left(\begin{array}{cc}-1&2\\-2&3\end{array}\right)$
evaluate $\textbf{CC}^T$.

\bigskip

ANSWER

\begin{eqnarray*}
\textbf{CC}^T&=&\left(\begin{array}{cc}-1&2\\-2&3\end{array}\right)
\left(\begin{array}{cc}-1&-2\\2&3\end{array}\right)\\
&=&\left(\begin{array}{cc}-1(-1)+2(2)&-1(-2)+2(3)\\-2(-1)+3(2)&-2(-2)+3(3)\end{array}\right)\\
&=&\left(\begin{array}{cc}1+4&2+6\\2+6&4+9\end{array}\right)\\
&=&\left(\begin{array}{cc}5&8\\8&13\end{array}\right)
\end{eqnarray*}




\end{document}