Bentuk Sin (2x-3phi/2) – Sin (4x+phi/2) Ekuivalen Dengan…..

Sin (2x-3π/2) – Sin (4x+π/2)
= (sin 2x.cos 3π/2 – cos 2x.sin 3π/2) – (sin 4x.cos π/2 + cos 4x.sin π/2)
= (sin 2x.(0) – cos 2x.(-1)) – (sin 4x.(0) + cos 4x.(1))
= cos 2x – cos 4x