Hệ thức nào sau đây là sai?

A. \({\rm{cos5}}\alpha {\rm{.cos2}}\alpha  = \frac{1}{2}\left( {{\rm{cos}}7\alpha  + {\rm{cos}}3\alpha } \right).\)

B. \(\sin 5\alpha \cos 2\alpha  = \frac{1}{2}\left( {\sin 3\alpha  + \sin 7\alpha } \right).\)

C. \({\rm{sin6}}\alpha .\sin 2\alpha  = \frac{1}{2}\left( {\cos 4\alpha  - \cos 8\alpha } \right).\)

D. \({\rm{cos2}}\alpha {\rm{.sin5}}\alpha  = \frac{1}{2}\left( {\sin 7\alpha  - \sin 3\alpha } \right).\)