(a)[4]
Demonstrate that $\cos 4x + 2\sin^2 x - 1 = 8\sin^4 x - 6\sin^2 x$.
(b)[4]
Hence solve the equation $\cos 4x + 2\sin^2 x - 1 = 0$ for $-180^\circ \leq x \leq 180^\circ$.
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: “Apply the correct double-angle formula to write $\cos4x$ in terms of $\sin^22x$” …
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