Prove that :

i.

ii.

iii.

i. We know, 2 sin A sin B = cos (A – B) – cos (A + B)

= cos 60° - cos 90°

Hence Proved

ii. We know, 2 cos A cos B = cos (A + B) + cos (A – B)

= cos 90° + cos 60°

Hence Proved

iii. We know, 2 sin A cos B = sin (A + B) + sin (A – B)

= sin 90° + sin 60°

Hence Proved