6 The matrix \(\mathbf { A }\) is defined by
$$\mathbf { A } = \left( \begin{array} { r r r r }
1 & - 1 & - 2 & - 3
- 2 & 1 & 7 & 2
- 3 & 3 & 6 & \alpha
7 & - 6 & - 17 & - 17
\end{array} \right) .$$
- Show that if \(\alpha = 9\) then the rank of \(\mathbf { A }\) is 2, and find a basis for the null space of \(\mathbf { A }\) in this case.
- Find the rank of \(\mathbf { A }\) when \(\alpha \neq 9\).