$(a)\;2(cos \large\frac{\pi}{3}+ i sin\large\frac{\pi}{3})\qquad(b)\;2(cos \large\frac{\pi}{5}+ i sin\large\frac{\pi}{5})\qquad(c)\;(cos \large\frac{\pi}{3}+ i sin\large\frac{\pi}{3})\qquad(d)\;0$