Answer
$\frac{-3\sqrt 3}{2}+\frac{3}{2}i$
Work Step by Step
$3$ cis $150^{\circ}$=$3(\cos150^{\circ}+i\sin150^{\circ})$
It is known that $\cos150^{\circ}=-\frac{\sqrt 3}{2}$ and $\sin150^{\circ}=\frac{1}{2}$
Substituting these values in the expression and solving:
$3(\cos150^{\circ}+i\sin150^{\circ})=3(-\frac{\sqrt 3}{2}+\frac{1}{2}i)=\frac{-3\sqrt 3}{2}+\frac{3}{2}i$
