(\cos\theta+i\sin\theta)^{4}=\cos4\theta+i\sin4\theta \,\, [By \,\, De \,\, Moivre's \,\, Theorem] \\\\ By \,\, the \,\, Binomial \,\, Theorem, \,\, (\cos\theta+i\sin\theta)^{4}=\cos^{4}\theta+4i\sin\theta\cos^{3}\theta-6\sin^{2}\theta\cos^{2}\theta-4i\sin^{3}\theta\cos\theta+\sin^{4}\theta \\\\...