Question

2(1 – 2 sin² 7x) sin 3x is equal to

A. sin 17x – sin 11x

B. sin 11x – sin 17x

C. cos 17x – cos 11x

D. cos 17x + cos 11x

Answer 1

Correct answer is A.

Given expression is 2(1 – 2 sin² 7x) sin 3x

2(1 – 2 sin² 7x) sin 3x = 2 cos 2(7x) sin 3x

[using cos 2A = 1 – 2sin²A]

= 2 cos 14x sin 3x

Therefore 2(1 – 2 sin² 7x) sin 3x = sin (17x) – sin (11x)