4 The position vectors of points \(A\) and \(B\) are \(\left( \begin{array} { r } - 3
6
3 \end{array} \right)\) and \(\left( \begin{array} { r } - 1
2
4 \end{array} \right)\) respectively, relative to an origin \(O\).
- Calculate angle \(A O B\).
- The point \(C\) is such that \(\overrightarrow { A C } = 3 \overrightarrow { A B }\). Find the unit vector in the direction of \(\overrightarrow { O C }\).