Question

Express 2 cos 4x sin 2x as an algebraic sum of sines and cosines.

Answer 1

Using, 

2 cos A sin B = sin (A + B) – sin (A – B) 

We get 

2 cos 4x sin 2x = sin (4x + 2x) – sin (4x - 2x) 

= sin 6x – sin 2x