9 Two lines have vector equations
$$\mathbf { r } = \left( \begin{array} { r }
4
2
- 6
\end{array} \right) + t \left( \begin{array} { r }
- 8
1
- 2
\end{array} \right) \quad \text { and } \quad \mathbf { r } = \left( \begin{array} { r }
- 2
a
- 2
\end{array} \right) + s \left( \begin{array} { r }
- 9
2
- 5
\end{array} \right) ,$$
where \(a\) is a constant.
- Calculate the acute angle between the lines.
- Given that these two lines intersect, find \(a\) and the point of intersection.