Prove 2cosx - cos3x - cos5x = 16cos^3x*sin^2x
cosx - cos3x + cosx - cos5x
-2 sin 2x sin (-x)+ [-2 sin 3x sin (-2x)]
2 sin2x [sinx + sin3x]
2 sin 2x.2 sin2x cosx
16 sin^ 2x .cos^ 3x
-2 sin 2x sin (-x)+ [-2 sin 3x sin (-2x)]
2 sin2x [sinx + sin3x]
2 sin 2x.2 sin2x cosx
16 sin^ 2x .cos^ 3x