5. The line \(l _ { 1 }\) has equation \(\mathbf { r } = \left( \begin{array} { r } 1
0
- 1 \end{array} \right) + \lambda \left( \begin{array} { l } 1
1
0 \end{array} \right)\). The line \(l _ { 2 }\) has equation \(\mathbf { r } = \left( \begin{array} { l } 1
3
6 \end{array} \right) + \mu \left( \begin{array} { r } 2
1
- 1 \end{array} \right)\).

1. Show that \(l _ { 1 }\) and \(l _ { 2 }\) do not meet. The point \(A\) is on \(l _ { 1 }\) where \(\lambda = 1\), and the point \(B\) is on \(l _ { 2 }\) where \(\mu = 2\).
2. Find the cosine of the acute angle between \(A B\) and \(l _ { 1 }\).