The points A, B, C have position vectors i-2k, i+2j+2k, 2i-j-k, respectively.
- (a)Find the equation of the plane ABC, giving your answer in the form ax+by+cz = d.[5]
- (b)A point D has position vector i+tk, where t≠-2. Find the acute angle between the planes ABC and ABD.[4]
- (c)Find the values of t such that the shortest distance between the lines AB and CD is √2.[7]
Mark scheme
Marking points from the official mark scheme (May/June 2025). The mark or mark type is shown in brackets.
- [B1] Finds direction vectors of two lines in the plane.
- [M1 A1] Finds normal to the plane ABC.
- [M1 A1] Substitutes point.
- [M1 A1] Finds normal to the plane ABD.
- [M1] Uses dot product of normal vectors in correct formula.
- [A1] 0.641 rad.
- [M1 A1] Finds common perpendicular.
- [M1 A1] Uses formula for perpendicular distance.
- [M1] Sets equal to √2 and solves for t.
- [A1 A1] t = 6.83, t = 1.17.
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