Relative to an origin O, the position vectors of points A and B are given by OA = 2i – 5j – 2k and OB = 4i – 4j + 2k. The point C is such that AB = BC. Find the unit vector in the direction of OC.
- Relative to an origin O, the position vectors of points A and B are given by OA = 2i – 5j – 2k and OB = 4i – 4j + 2k. The point C is such that AB = BC. Find the unit vector in the direction of OC.[4]
Mark scheme
Marking points from the official mark scheme (May/June 2016). The mark or mark type is shown in brackets.
- [B1] AB = 2i + j +4k or AC = 4i + 2j + 8k
- [M1] OC = OA+ AC = 6i -3j + 6k correct method for OC
- OR
- [B1] (x-4) = 2 (y+4) = 1 (z-2) = 4
- [M1] OC = y= -3 z= 6
- OR
- [B1] OB – OA = OC – OB .: OC = 2OB – OA
- [M1] Divides by their mod of their OC
- [A1] = (6i -3j + 6k) ÷ 9 Correct unsimplified expression
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