4 Relative to an origin \(O\), the points \(A\) and \(B\) have position vectors \(3 \mathbf { i } + 2 \mathbf { j } + 3 \mathbf { k }\) and \(\mathbf { i } + 3 \mathbf { j } + 4 \mathbf { k }\) respectively.
- Find a vector equation of the line passing through \(A\) and \(B\).
- Find the position vector of the point \(P\) on \(A B\) such that \(O P\) is perpendicular to \(A B\).