Find the Product $\left[ 4 \operatorname { cis } 30 ^ { \circ } \right] \left[ 5 \operatorname { cis } 120 ^ { \circ } \right]$

Multiple Choice

Find the product. Write the product in rectangular form, using exact values.
- $\left[ 4 \operatorname { cis } 30 ^ { \circ } \right] \left[ 5 \operatorname { cis } 120 ^ { \circ } \right]$

A) $10 + 10 \sqrt { 3 } \mathrm { i }$
B) $- 10 \sqrt { 3 } + 10 \mathrm { i }$
C) $10 \sqrt { 3 } - 10 \mathrm { i }$
D) $- 10 - 10 \sqrt { 3 } i$