Question

How do you Prove: sin θ - sin θ•cos2 θ = sin3 θ.

Answer 1

sin θ - sin θ•cos2 θ

=sin θ( 1- cos2 θ)

=sin θ (1-cos^2 θ+sin^2 θ)

=sinθ(2sin^2 θ)

=2sin^3 θ