Question #a07f3
1 Answer
Oct 22, 2015
Prove sin x.sin 2x + cos x.cos 2x = cos (x)
Explanation:
Use the trig identity: cos (a - b) = sin a.sin b + cos a.cos b.
Therefor:
cos x = cos (2x - x) = sin x.sin 2x + cos x.cos 2x.
