(i)[3]
Demonstrate that $\cos(\theta - 60^\circ) + \cos(\theta + 60^\circ) = \cos \theta$.
(ii)[4]
If $\dfrac{\cos(2x - 60^\circ) + \cos(2x + 60^\circ)}{\cos(x - 60^\circ) + \cos(x + 60^\circ)} = 3$, determine the exact value of $\cos x$.
Mathematics 9709 · AS & A Level · Trigonometry
Trigonometry — practice question
Worked solution & mark scheme
This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Apply $\cos(A+B)$ correctly at least once, or use the $\cos A+\cos B$ formula” …
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