Answer
\[\left[ {\begin{array}{*{20}{c}}
3&{ - 4\sqrt 7 } \\
{4\sqrt 7 }&{ - 8}
\end{array}} \right]\]
Work Step by Step
\[\begin{gathered}
\left[ {\begin{array}{*{20}{c}}
2&{\sqrt 7 } \\
{3\sqrt {28} }&{ - 6}
\end{array}} \right] - \left[ {\begin{array}{*{20}{c}}
{ - 1}&{5\sqrt 7 } \\
{2\sqrt 7 }&2
\end{array}} \right] \hfill \\
{\text{Use the scalar multiplication}} \hfill \\
= \left[ {\begin{array}{*{20}{c}}
2&{\sqrt 7 } \\
{3\sqrt {4 \cdot 7} }&{ - 6}
\end{array}} \right] + \left[ {\begin{array}{*{20}{c}}
1&{ - 5\sqrt 7 } \\
{ - 2\sqrt 7 }&{ - 2}
\end{array}} \right] \hfill \\
= \left[ {\begin{array}{*{20}{c}}
2&{\sqrt 7 } \\
{6\sqrt 7 }&{ - 6}
\end{array}} \right] + \left[ {\begin{array}{*{20}{c}}
1&{ - 5\sqrt 7 } \\
{ - 2\sqrt 7 }&{ - 2}
\end{array}} \right] \hfill \\
{\text{Add the corresponding elements}} \hfill \\
= \left[ {\begin{array}{*{20}{c}}
{2 + 1}&{\sqrt 7 - 5\sqrt 7 } \\
{6\sqrt 7 - 2\sqrt 7 }&{ - 6 - 2}
\end{array}} \right] \hfill \\
{\text{Simplify}} \hfill \\
= \left[ {\begin{array}{*{20}{c}}
3&{ - 4\sqrt 7 } \\
{4\sqrt 7 }&{ - 8}
\end{array}} \right] \hfill \\
\end{gathered} \]
