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\begin{document}

{\bf Question}

Evaluate $A+B,\ A-B$ and $B-A$ where

\begin{description}
\item[(i)]
$A=\left(\begin{array}{cc} 2 & 1\\ 9 & 7\end{array}\right);\ \
B=\left(\begin{array} {cc} -6 & 3\\ 1 & 8 \end{array} \right)$

\item[(ii)]
$A=\left(\begin{array}{cc} 7 & 1\\ -3 & 6\\ 6 & -3
\end{array}\right);\ \ B=\left(\begin{array} {cc} 2 & 6\\ 1 & -8\\
2 & 4 \end{array} \right)$
\end{description}

\medskip

{\bf Answer}
\begin{description}
\item[(i)]
$A+B=\left(\begin{array}{cc} 2 & 1\\9 & 7
\end{array}\right)+\left(\begin{array}{cc} -6 & 3\\1 & 8
\end{array}\right)=\left(\begin{array}{cc} -4 & 4\\10 & 15
\end{array}\right)$

$A-B=\left(\begin{array}{cc} 2 & 1\\9 & 7
\end{array}\right)-\left(\begin{array}{cc} -6 & 3\\1 & 8
\end{array}\right)=\left(\begin{array}{cc} 8 & -2\\8 & -1
\end{array}\right)$

$B-A=-(A-B)=\left(\begin{array}{cc} -8 & 2\\-8 & 1
\end{array}\right)$

\item[(ii)]
$A+B=\left(\begin{array}{cc} 7 & 1\\-3 & 6\\6 & -3
\end{array}\right)+\left(\begin{array}{cc} 2 & 6\\1 & -8\\ 2 & 4
\end{array}\right)=\left(\begin{array}{cc} 9 & 7\\-2 & -2\\ 8 & +1
\end{array}\right)$

$A-B=\left(\begin{array}{cc} 7 & 1\\-3 & 6\\6 & -3
\end{array}\right)-\left(\begin{array}{cc} 2 & 6\\1 & -8\\ 2 & 4
\end{array}\right)=\left(\begin{array}{cc} 5 & -5\\-4 & 14\\ 4 & -7
\end{array}\right)$

$B-A=-(A-B)=\left(\begin{array}{cc} -5 & 5\\4 & -14\\-4 & 7
\end{array}\right)$

\end{description}

\end{document}