Answer
(a) $ 2+2\sqrt 3\ i$,
(b) $ -3.2139+3.8302i$,
(c) $ -7i$
Work Step by Step
(a) $4(cos60^\circ+i\ sin60^\circ)=4(\frac{1}{2}+i\ \frac{\sqrt 3}{2})=2+ 2\sqrt 3\ i$,
(b) $5cis130^\circ=5(cos130^\circ+i\ sin130^\circ)\approx-3.2139+3.8302i$,
(c) $7(cos270^\circ+i\ sin270^\circ)=7(0-i)=-7i$
