Answer
\[\left[ {\begin{array}{*{20}{c}}
{2\sqrt {21} }&{ - 7} \\
{4\sqrt 3 }&{ - 14\sqrt 7 }
\end{array}} \right]\]
Work Step by Step
\[\begin{gathered}
\left[ {\begin{array}{*{20}{c}}
{\sqrt 7 }&0 \\
2&{\sqrt {28} }
\end{array}} \right]\left[ {\begin{array}{*{20}{c}}
{2\sqrt 3 }&{ - \sqrt 7 } \\
0&{ - 6}
\end{array}} \right] \hfill \\
{\text{Multiply elements of each row of each column of }}A{\text{ by }} \hfill \\
{\text{elements of each column of }}B \hfill \\
AB = \left[ {\begin{array}{*{20}{c}}
{\left( {\sqrt 7 } \right)\left( {2\sqrt 3 } \right) + \left( 0 \right)\left( 0 \right)}&{\left( {\sqrt 7 } \right)\left( { - \sqrt 7 } \right) + \left( 0 \right)\left( { - 6} \right)} \\
{\left( 2 \right)\left( {2\sqrt 3 } \right) + \left( {\sqrt {28} } \right)\left( 0 \right)}&{\left( 2 \right)\left( { - \sqrt 7 } \right) + \left( {\sqrt {28} } \right)\left( { - 6} \right)}
\end{array}} \right] \hfill \\
{\text{Simplify}} \hfill \\
AB = \left[ {\begin{array}{*{20}{c}}
{2\sqrt {21} }&{ - 7} \\
{4\sqrt 3 }&{ - 14\sqrt 7 }
\end{array}} \right] \hfill \\
\end{gathered} \]
