Answer
(a) $ \frac{3\sqrt 3}{2}+\frac{3}{2}i$
(b) $ 3.06+2.57i$
(c) $ 3i$
Work Step by Step
(a) $3(cos30^\circ+i\ sin30^\circ)=3(\frac{\sqrt 3}{2}+i\ \frac{1}{2})=\frac{3\sqrt 3}{2}+\frac{3}{2}i$
(b) $4cis40^\circ=4(cos40^\circ+i\ sin40^\circ)=4cos40^\circ+i\ 4sin40^\circ\approx3.06+2.57i$
(c) $3(cos90^\circ+i\ sin90^\circ)=3(0+i )=3i$
