Answer
$$ - 10 + 0i$$
Work Step by Step
$$\eqalign{
& \left[ {5\left( {\cos 150^\circ + i\sin 150^\circ } \right)} \right]\left[ {2\left( {\cos 30^\circ + i\sin 30^\circ } \right)} \right] \cr
& = \left( 5 \right)\left( 2 \right)\left( {\cos \left( {150^\circ + 30^\circ } \right) + i\sin \left( {150^\circ + 30^\circ } \right)} \right) \cr
& = 10\left( {\cos \left( {180^\circ } \right) + i\sin \left( {180^\circ } \right)} \right) \cr
& = 10\left( { - 1 + i\left( 0 \right)} \right) \cr
& = - 10 + 0i \cr} $$
