## nickersia Group Title Use De Moivre's Theorem to prove the identity: 3 months ago 3 months ago

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1. nickersia Group Title

$\cos 3\alpha=4\cos ^{3}\alpha-3\cos \alpha$

2. nickersia Group Title

Anyone?

3. BSwan Group Title

simply De Moivre's Theorem :- $$(\cos x+ i \sin x)^n=\cos (nx ) +i \sin(nx)$$