Mathematics 9709 · AS & A Level · Trigonometry

Trigonometry — practice question

(a)[6]

Express $3\sin 2\theta \sec \theta + 10\cos(\theta - 30^\circ)$ in the form $R\sin(\theta + \alpha)$ where $R > 0$ and $0^\circ < \alpha < 90^\circ$. Give the value of $\alpha$ correct to 2 decimal places.

(b)[3]

Hence, solve the equation $3\sin 4\beta \sec 2\beta + 10\cos(2\beta - 30^\circ) = 2$ for $0^\circ < \beta < 90^\circ$.

Worked solution & mark scheme

This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: Apply $\sin2\theta=2\sin\theta\cos\theta$ and $\sec\theta=\tfrac1{\cos\theta}$ to get $6\sin\theta$

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