Mathematics 9709 · AS & A Level · Trigonometry

Trigonometry — practice question

(i)[3]

If $\sec \theta + 2\cosec \theta = 3\cosec 2\theta$, prove that $2\sin \theta + 4\cos \theta = 3$.

(ii)[3]

Write $2\sin \theta + 4\cos \theta$ in the form $R\sin(\theta + \alpha)$ with $R > 0$ and $0^\circ < \alpha < 90^\circ$, and give $\alpha$ correct to $2$ decimal places.

(iii)[4]

Hence solve $\sec \theta + 2\cosec \theta = 3\cosec 2\theta$ for $0^\circ < \theta < 360^\circ$.

Worked solution & mark scheme

This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: Replace $\sec\theta$ by $\dfrac1{\cos\theta}$ and $\cosec\theta$ by $\dfrac1{\sin\theta}$

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