Paper 1 · Trigonometry

Given $f(x) = \cos 2x - \cos x$ , the derivative $f'(x)$ factorises as

A

\sin x(4\cos x - 1)

B

\cos x(1 - 4\sin x)

C

\sin x(1 - 4\cos x)

D

-2\sin 2x \cos x

Explanation:

f'(x) = -2\sin2x + \sin x = -4\sin x\cos x + \sin x = \sin x(1-4\cos x)

.

Derived from ZIMSEC Mathematics Paper 1, June 2011, Q11

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