Question

Sin4θ - sin2θ = _____

2cos3θcosθ
2cos3θsinθ
2sin3θcosθ
2sin3θsinθ

Answer 1

B. 2cos3θsinθ.

Explanation:

Use the identity

sin x - sin y = 2 [cos(x + y)/2]sin [x - y)/2].

So we have:

sin4θ - sin2θ = 2 cos (4θ+2θ)/2 sin (4θ-2θ)/2

= 2cos3θsinθ.