Using the operator \(a=1 / 120^{\circ}\), evaluate the following in polar form:

(a) \((a-1) /\left(1+a-a^{2}ight)\),

(b) \(\left(a^{2}+a+jight) /\left(j a+a^{2}ight)\),

(c) \((1+a)\left(1+a^{2}ight)\), and

(d) \(\left(a-a^{2}ight)\left(a^{2}-1ight)\).