Answer
$\begin{bmatrix}
1 & 0 & 0\\
0 & 1 & 0\\
0 & 0 & 1
\end{bmatrix}$
Work Step by Step
Using a Calculator:
$\begin{bmatrix}
-1 & 2 & 1\\
3 & 4 & 9\\
2 & 1 & -2
\end{bmatrix}$ ~ $\begin{bmatrix}
1 & 0 & 0\\
0 & 1 & 0\\
0 & 0 & 1
\end{bmatrix}$
