Answer
$$AA=\left[\begin{array}{rrr}{4} & {0} & {0} \\ {0} & {9} & {0} \\ {0} & {0} & {0}\end{array}\right] $$
Work Step by Step
Given
$$
A=\left[\begin{array}{rrr}{2} & {0} & {0} \\ {0} & {-3} & {0} \\ {0} & {0} & {0}\end{array}\right]
$$
We have
\begin{align*}
AA&= \left[\begin{array}{rrr}{2} & {0} & {0} \\ {0} & {-3} & {0} \\ {0} & {0} & {0}\end{array}\right]\left[\begin{array}{rrr}{2} & {0} & {0} \\ {0} & {-3} & {0} \\ {0} & {0} & {0}\end{array}\right]\\
&=\left[\begin{array}{rrr}{4} & {0} & {0} \\ {0} & {9} & {0} \\ {0} & {0} & {0}\end{array}\right]
.
\end{align*}