9.
The position vectors of three points \(A , B\) and \(C\) relative to an origin \(O\) are given respectively by
$$\text { and } \quad \begin{aligned}
& \overrightarrow { O A } = 7 \mathbf { i } + 3 \mathbf { j } - 3 \mathbf { k } ,
& \overrightarrow { O B } = 4 \mathbf { i } + 2 \mathbf { j } - 4 \mathbf { k }
& \overrightarrow { O C } = 5 \mathbf { i } + 4 \mathbf { j } - 5 \mathbf { k } .
\end{aligned}$$
- Find the angle between \(A B\) and \(A C\).
- Find the area of triangle \(A B C\).