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\newcommand{\ds}{\displaystyle}
\newcommand{\pl}{\partial}
\parindent=0pt
\begin{document}


{\bf Question}

Find the inverses of

\begin{description}
\item[(i)] $\ds \left( \begin{array}{ccc}2 & 4 & 1 \\ 1 & 1 & 1 \\ 2 & 3 & 1
 \end{array} \right)$

\item[(ii)]$\ds \left( \begin{array}{ccc} 5 & 15 & -10 \\ -2 & -2 & -4 \\ 3 & 4 & 1
\end{array} \right)$
\item[(iii)]$\ds \left( \begin{array}{cccc} 1 & -2 & 1 & -5 \\ 3 & -6 & 4 & -14 \\
-2 & 4 & -4 & 9 \\ 4 & -7 & 5 & -18 \end{array} \right) $
\end{description}

Check your answer by multiplication.

\vspace{.25in}

{\bf Answer}

\begin{description}
\item[(i)] Inverse $ = \left( \begin{array}{ccc} -2 & -1 & 3 \\ 1 & 0 & -1
\\ 1 & 2 & -2\end{array} \right)$
\item[(ii)] Inverse $\ds = \left( \begin{array}{ccc} \ds -\frac{7}{30} &  \ds \frac{11}{12} &  \ds \frac{4}{3}
\\ \\ \ds \frac{5}{30} &  \ds -\frac{7}{12} &  \ds -\frac{2}{2} \\ \\ \ds \frac{1}{30} &
\ds -\frac{5}{12} &  \ds -\frac{1}{3} \end{array} \right)$
\item[(iii)] Inverse $ = \left( \begin{array}{cccc} -14 & 5 & 4 & 2 \\
3 & -3 & -1 & 1 \\ 1 & -1 & -1 & 0 \\ -4 & 2 & 1 & 0 \end{array}
\right)$
\end{description}


\end{document}