(i)[4]
Prove that $\cos 3\theta = 4\cos^3 \theta - 3\cos \theta$.
(ii)[4]
From this result, find the exact value of $\int_{\frac{\pi}{4}}^{\frac{3\pi}{4}} \cos^3 \theta\, d\theta$.
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: “Use the correct $\cos(A+B)$ formula to write $\cos3\theta$ in terms of trig functions of $2\theta$ and $\theta$” …
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