Hasil integral -π sampai 1/3π cos (2x +1/3π)dx... .

dsin (2x + 1/3 π) /dx = 2 cos (2x + 1/3 π)
cos (2x + 1/3 π) dx = 1/2 dsin (2x + 1/3 π)

∫cos (2x + 1/3 π) dx [1/3 π ... -π]
= 1/2 ∫dsin (2x + 1/3 π)
= 1/2 sin (2x + 1/3 π)
= 1/2 [sin (2.(1/3 π) + 1/3 π) - sin (2(-π) + 1/3 π)]
= 1/2 [sin π + sin 5/3 π)]
= 1/2 [sin 180° + sin 300°]
= 1/2 [ 0 - 1/2 √3]
= -1/4 √3