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Use a scalar product to determine angle $ACB$.
Mathematics 9709 · AS & A Level · Coordinate geometry
Coordinate geometry — practice question
The diagram depicts a pyramid $OABC$ with a flat base $OAB$ such that $OA = 6\,\text{cm}$, $OB = 8\,\text{cm}$ and $\angle AOB = 90^{\circ}$. Point $C$ lies vertically above $O$ and $OC = 10\,\text{cm}$. The unit vectors $\mathbf{i}$, $\mathbf{j}$ and $\mathbf{k}$ are parallel to $OA$, $OB$ and $OC$ respectively, as illustrated.