A-LevelMathematicsDifferentiation9709/32 · May/June 2020 · Q46 Marks
A curve has equation y = cos x sin 2x. Find the x-coordinate of the stationary point in the interval 0 < x < ½π, giving your answer correct to 3 significant figures.
- (a)Find the x-coordinate of the stationary point in the interval 0 < x < ½π, giving your answer correct to 3 significant figures.[6]
Mark scheme
Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.
- [M1] Use correct product rule
- [A1] Obtain correct derivative in any form, e.g. –sin x sin 2x + 2cos x cos 2x
- [M1] Use double angle formula to express derivative in terms of sin x and cos x
- [M1] Equate derivative to zero and obtain an equation in one trig function
- [A1] Obtain 3 sin² x = 1, or 3 cos² x = 2 or 2 tan² x = 1
- [A1] Solve and obtain x = 0.615
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