hasil dari integral 1. 3 cos 2x cos x dx 2. cos 7x cos 2x dx

∫3cos 2x cos x dx
= 3∫cos 2x dsin x
= 3∫(1 - 2sin² x) dsin x
= 3(∫dsin x - 2∫sin² x dx)
= 3(sin x - (2/3)sin³ x) + c
= 3sin x - 2sin³ x + c

∫cos 7x cos 2x dx
= (1/2)(∫(cos 9x) dx + ∫(cos 5x) dx)
= (1/2)(1/9)sin 9x + (1/2)(1/5)sin 5x + c
= (1/18)sin 9x + (1/10)sin 5x + c