DB45
Ubah bentuk sin x cos x cos 3x = 1/2 ( sin 2x ) . cos 3x = 1/2 . cos 3x . sin 2x = 1/4 ( 2 . cos 3x . sin 2x) = 1/4 (sin 5x - sin x) = 1/4 sin 5x - 1/4 sin x
∫(π/₃ ....0) 1/4 sin 5x - 1/4 sin x dx = -1/20 cos 5x + 1/4 cos x ](π/₃...0) = -1/20 (cos 5π/3 - cos 0) + 1/4 ( cos π/3 - cos 0) = - 1/20 (1/2 - 1) + 1/4 (1/2 - 1) = -1/20 (-1/2) + 1/4(-1/2) = 1/40 - 1/8 = 1/40 - 5/40 = - 4/40 = - 1/10
= 1/2 . cos 3x . sin 2x
= 1/4 ( 2 . cos 3x . sin 2x)
= 1/4 (sin 5x - sin x)
= 1/4 sin 5x - 1/4 sin x
∫(π/₃ ....0) 1/4 sin 5x - 1/4 sin x dx
= -1/20 cos 5x + 1/4 cos x ](π/₃...0)
= -1/20 (cos 5π/3 - cos 0) + 1/4 ( cos π/3 - cos 0)
= - 1/20 (1/2 - 1) + 1/4 (1/2 - 1)
= -1/20 (-1/2) + 1/4(-1/2)
= 1/40 - 1/8
= 1/40 - 5/40
= - 4/40
= - 1/10