mohon bantuannyaa + caranyaa

jawab
4 cos³ x = cos 3x + 3 cos x

(0...π/2)  ∫ 4 cos³ x dx =  
(0...π/2)  ∫ cos 3x + 3 cos x dx

= 1/3 sin 3x + 3 sin x ]π/2...0

= 1/3 ( sin 3π/2 - sin 0) + 3 (sin π/2 - sin 0)
= 1/3 (-1) + 3(1 -0)
= - 1/3 + 3
= 8/3