Relative to an origin \(O\), the position vectors of the points \(A\), \(B\) and \(C\) are given by
$$\overrightarrow{OA} = \begin{pmatrix} 2 \\ -1 \\ 4 \end{pmatrix}, \quad \overrightarrow{OB} = \begin{pmatrix} 4 \\ 2 \\ -2 \end{pmatrix} \quad \text{and} \quad \overrightarrow{OC} = \begin{pmatrix} 1 \\ 3 \\ p \end{pmatrix}.$$
Find
- the unit vector in the direction of \(\overrightarrow{AB}\), [3]
- the value of the constant \(p\) for which angle \(BOC = 90°\). [2]