Berapakah 3 cis 120• + 4 cis 270•=

Bilangan Kompleks.

cis θ = cos θ + i sin θ

3 cis 120° + 4 cis 270°
= 3(cos 120° + i sin 120°) + 4(cos 270° + i sin 270°)
= 3(-1/2 + 1/2 i√3) + 4[0 + i (-1)]
= -3/2 + 3/2 i√3 - 4i
= -3/2 - 5/2 i√3