0606 P13 - Jun 2023 - Q10 - 8 marks
7682
(a) Show that
\(\cos^4\theta-\sin^4\theta+1=2\cos^2\theta.\)
(b) Solve the equation
\(\cos^4\frac{\phi}{3}-\sin^4\frac{\phi}{3}+1=\frac12,\)
for \(-3\pi\lt\phi\lt3\pi\), giving your answers in terms of \(\pi\).
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