JEE Advance - Mathematics (1986 - No. 4)

The expression $$2\left[ {{{\sin }^6}\left( {{\pi \over 2} + \alpha } \right) + {{\sin }^6}\left( {5\pi - \alpha } \right)} \right]$$ is equal to

$$\sin \,4\,\alpha + \cos \,6\,\alpha \,\,\,\,$$