CAPE Pure Mathematics Unit 1 · May/June 2010 · Paper 1 · Question Q28
\vec{OP} and \vec{OQ} are two vectors such that \vec{OP} = \mathbf{r} - \mathbf{s} and \vec{OQ} = 2\mathbf{r} + 3\mathbf{s}. Given that \vec{OP} is perpendicular to \vec{OQ} then \mathbf{r}\cdot\mathbf{s} is equal to
- (A)
3s^2 - 2r^2 - (B)
3s - 2r - (C)
rs - (D)
6rs
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