Answer:
-i.
Step-by-step explanation:
Applying DeMoivre' s theorem:
(sin 30 + i cos 30)^18
= sin(18*30) + i cos(18*30)
= sin 540 + i cos 540
= sin (3*180) + i cos (3*180)
= 0 + -1 * i
= -i.
