Answer
$$ - 2 - 2\sqrt 3 i$$
Work Step by Step
$$\eqalign{
& 4\operatorname{cis} 240^\circ \cr
& {\text{Write in trigonometric form}} \cr
& = 4\left( {\cos 240^\circ + i\sin 240^\circ } \right) \cr
& {\text{Calculate }}\cos 240^\circ {\text{ and }}\sin 240^\circ \cr
& \cos 240^\circ = - \frac{1}{2} \cr
& \sin 240^\circ = - \frac{{\sqrt 3 }}{2} \cr
& {\text{,then}} \cr
& 4\left( {\cos 240^\circ + i\sin 240^\circ } \right) = 4\left( { - \frac{1}{2} - \frac{{\sqrt 3 }}{2}i} \right) \cr
& = - 2 - 2\sqrt 3 i \cr} $$
