In the diagram, OABCDEFG is a cube in which each side has length 6. Unit vectors i, j and k are parallel to OA, OC and OD respectively. The point P is such that AP = ⅓ AB and the point Q is the mid-point of DF. [Figure X.X]
- (i)Express each of the vectors OQ and PQ in terms of i, j and k.[3]
- (ii)Find the angle OQP.[4]
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Mark scheme
Marking points from the official mark scheme (Oct/Nov 2009). The mark or mark type is shown in brackets.
- [1] OQ = 3i + 3j + 6k (co)
- [2] PQ = -3i + j + 6k (Loses one for each error)
- [1] Use of x₁x₂ + y₁y₂ + z₁z₂ co. (e.g. 30)
- [1] Correct method for modulus (once) and all correctly linked. co.
- [2] θ = 53.0° (M1 for cosine rule, M1 for attempt at 3 sides, A1 for answer)
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