Chapter 2.6, Problem 3E

In Exercises $1-4$, show that the matrixes are inverses of each other by showing that their product is the identity matrix $I$.

$\left[\begin{array}{ccc}3& 2& 3\\ 2& 2& 1\\ 2& 1& 1\end{array}\right]$ and $\left[\begin{array}{ccc}-\frac{1}{3}& -\frac{1}{3}& \frac{4}{3}\\ 0& 1& -1\\ \frac{2}{3}& -\frac{1}{3}& -\frac{2}{3}\end{array}\right]$.