Answer
$-2-2i\sqrt 3$
Work Step by Step
$4$ cis $240^{\circ}=4(\cos 240^{\circ}+i\sin 240^{\circ})$
Using a calculator, we find that $\cos240^{\circ}=-\frac{1}{2}$ and $\sin240^{\circ}=-\frac{\sqrt 3}{2}$
Substituting these values in the expression and solving:
$4(\cos240^{\circ}+i\sin240^{\circ})=4(-\frac{1}{2}+-\frac{\sqrt 3}{2}i)=-2-2i\sqrt 3$
