6 marksComplex Numbers
CAPE Pure Mathematics Unit 2 · May/June 2008 (T&T) · Paper 2 · Question 5(c)(ii)
Use De Moivre's theorem for (\cos \theta + \mathrm{i} \sin \theta)^3 to show that \cos 3\theta = 4\cos^3 \theta - 3\cos \theta.
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