/**/
  4 sin x cos x - 2 sin 2x cos 2x /**/
= 4 sin x cos x - 2 * 2 sin x cos x * (cos^2 x - sin^2 x) /**/
= 4 sin x cos x - 4 sin x cos x * (sin^2 x + cos^2 x - 2 sin^2 x) /**/
= 4 sin x cos x - 4 sin x cos x * (1 - 2 sin^2 x) /**/
= 4 sin x cos x - 4 sin x cos x + 8 sin^3 x cos x /**/
= 8 sin^3 x cos x