In the diagram, OA = a, OB = 2b and AB : BC = 1 : 3 . OBD is a straight line. [Figure showing a triangle OAC with B on OC and D on OB extended, vectors a and 2b shown, NOT TO SCALE]
- (a)Express AB in terms of a and b.[1]
- (b)Show that OC = 8b-3a.[2]
- (c)AD=kOC. Find the value of k.[1]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2024). The mark or mark type is shown in brackets.
- [1] 2b – a final answer
- [2] [OC =] a + 4(2b - a) oe
- [2] or [OC =] 2b + 3(2b - a) oe
- [2] with correct working leading to [OC =] 8b - 3a
- [2] M1 for AC = 4(2b – a) or BC = 3(2b – a)
- [2] or AC = 4(their(2b – a))
- [2] or BC = 3(their(2b – a))
- [2] or for a correct route for OC seen e.g. [OC =] OA + AC oe
- [2] or [OC =] OB + BC oe
- [1] 1/3
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