The position vectors of the points A, B, C, D are i + j + 3k, 3i + 4j + 5k, -i + 3k, mj + 4k, respectively, where m is a constant.
- (i)Show that the lines AB and CD are parallel when m = 3/2.[1]
- (ii)Given that m ≠ 3/2, find the shortest distance between the lines AB and CD.[5]
- (iii)When m = 2, find the acute angle between the planes ABC and ABD, giving your answer in degrees.[6]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.
- [B1] Or shows if parallel, then m=3/2
- [M1A1] Finds common perpendicular using cross product.
- [M1] Uses formula for shortest distance.
- [A1]
- [M1A1] Finds normal to plane ABC (AEF).
- [A1] Finds normal to ABD (AEF).
- [M1A1FT] Uses formula for angle between two lines.
- [A1] CAO.
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