7 Given that \(\mathbf { a } = \left( \begin{array} { r } 2
- 2
1 \end{array} \right) , \mathbf { b } = \left( \begin{array} { l } 2
6
3 \end{array} \right)\) and \(\mathbf { c } = \left( \begin{array} { c } p
p
p + 1 \end{array} \right)\), find
- the angle between the directions of \(\mathbf { a }\) and \(\mathbf { b }\),
- the value of \(p\) for which \(\mathbf { b }\) and \(\mathbf { c }\) are perpendicular.