6 Relative to an origin \(O\), the position vectors of the points \(A\) and \(B\) are given by
$$\overrightarrow { O A } = 2 \mathbf { i } + 3 \mathbf { j } + 5 \mathbf { k } \quad \text { and } \quad \overrightarrow { O B } = 7 \mathbf { i } + 4 \mathbf { j } + 3 \mathbf { k }$$
- Use a scalar product to find angle \(O A B\).
- Find the area of triangle \(O A B\).