The parametric equations of a curve are x = 1 – cos θ, y = cos θ – ½ cos 2θ.
- (a)Show that dy/dx = –2 sin²(½θ).[5]
Mark scheme
Marking points from the official mark scheme (Feb/Mar 2022). The mark or mark type is shown in brackets.
- [1] State dx/dθ = sinθ or dy/dθ = -sinθ + ½ sin 2θ
- [1] Use dy/dx = (dy/dθ) / (dx/dθ)
- [1] Obtain correct answer in any form e.g. (-sinθ + ½ sin 2θ) / sinθ
- [1] Use double angle correctly to obtain dy/dx in terms of θ
- [1] Obtain the given answer with no errors seen – 2sin²(½θ)
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