(i)[4]
Prove that $\cos 4\theta - 4\cos 2\theta = 8\sin^4 \theta - 3$.
(ii)[4]
Hence solve the equation $\cos 4\theta = 4\cos 2\theta + 3$ over $0^\circ \leq \theta \leq 360^\circ$.
Mathematics 9709 · AS & A Level · Trigonometry
Trigonometry — practice question
Worked solution & mark scheme
This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Express $\cos 4\theta$ as a function of $\cos 2\theta$ and/or $\sin 2\theta$.” …
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