The value of $\cos ^3\left(\frac{\pi}{8}\right) \cos \left(\frac{3 \pi}{8}\right)+\sin ^3\left(\frac

Question

The value of $\cos ^3\left(\frac{\pi}{8}\right) \cos \left(\frac{3 \pi}{8}\right)+\sin ^3\left(\frac{\pi}{8}\right) \sin \left(\frac{3 \pi}{8}\right)$ is

Professor PC Thomas Classes · Answer

Simplify using $\cos^3 A \cos B + \sin^3 A \sin B$ and angle addition to get $1/(2\sqrt{2})$.