Question

(cos П/12 - sin П/12)*(cos^3 П/12 + sin^3 П/12)

Answer 1

$(\cos\frac{\pi}{12}-\sin\frac{\pi}{12})(\cos^3\frac{\pi}{12}+\sin^3\frac{\pi}{12})=(\cos\frac{\pi}{12}-\sin\frac{\pi}{12})(\cos\frac{\pi}{12}+\sin\frac{\pi}{12})\cdot\\ \\ \cdot(\cos^2\frac{\pi}{12}-\cos\frac{\pi}{12}\sin\frac{\pi}{12}+\sin^2\frac{\pi}{12})=(\cos^2\frac{\pi}{12}-\sin^2\frac{\pi}{12})(1-0.5\sin(2\cdot\frac{\pi}{12}))=\\ \\ =\cos(2\cdot\frac{\pi}{12})(1-0.5\sin(2\cdot\frac{\pi}{12}))=\cos\frac{\pi}{6}(1-0.5\sin\frac{\pi}{6})=\frac{\sqrt{3}}{2}(1-0.5\cdot0.5)=\frac{3\sqrt{3}}{8}$