9 The matrix \(\mathbf { A }\) is given by \(\mathbf { A } = \left( \begin{array} { r r r } 2 & - 1 & 1
0 & 3 & 1
1 & 1 & a \end{array} \right)\), where \(a \neq 1\).
- Find \(\mathbf { A } ^ { - 1 }\).
- Hence, or otherwise, solve the equations
$$\begin{array} { r }
2 x - y + z = 1
3 y + z = 2
x + y + a z = 2
\end{array}$$