10 The matrix \(\mathbf { D }\) is given by \(\mathbf { D } = \left( \begin{array} { r r r } a & 2 & 0
3 & 1 & 2
0 & - 1 & 1 \end{array} \right)\), where \(a \neq 2\).
- Find \(\mathbf { D } ^ { - 1 }\).
- Hence, or otherwise, solve the equations
$$\begin{aligned}
a x + 2 y & = 3
3 x + y + 2 z & = 4
- y + z & = 1
\end{aligned}$$