Mathematics 9709 · AS & A Level · Coordinate geometry

Coordinate geometry — practice question

The figure depicts triangle $OAB$, where the position vectors of $A$ and $B$ relative to $O$ are $\vec{OA} = 2\mathbf{i} + \mathbf{j} - 3\mathbf{k}$ and $\vec{OB} = -3\mathbf{i} + 2\mathbf{j} - 4\mathbf{k}$. $C$ lies on $OA$ such that $\vec{OC} = p\vec{OA}$, with $p$ a constant.
(i)[4]

Find the angle $AOB$.

(ii)[1]

Find $\vec{BC}$ expressed in terms of $p$ and vectors $\mathbf{i}$, $\mathbf{j}$ and $\mathbf{k}$.

(iii)[4]

Find the value of $p$, given that $BC$ is perpendicular to $OA$.

Worked solution & mark scheme

This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: Compute the scalar product $\vec{OA}\cdot\vec{OB}=8$

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