(a)[4]
Show that $\cos 4\theta + 4\cos 2\theta + 3 = 8\cos^4 \theta$.
(b)[3]
Hence solve $\cos 4\theta + 4\cos 2\theta = 4$ for $0^\circ \leq \theta \leq 180^\circ$.
Mathematics 9709 · AS & A Level · Trigonometry
Trigonometry — practice question
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This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Write $\cos 4\theta$ in terms of $\cos 2\theta$ and/or $\sin 2\theta$” …
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