Answer:
18(cos(4pi/3) + i sin(4pi/3))
Explanation:
step 1: find the modulus (|z|=√(a^2 + b^2)
|z|=√((-9)^2+(-9√3)^2)= 81+243= 324 => √324=18
step 2: find the argument using theta =tan^-1 (y/x)
theta=tan^-1((-9√3)/-9) = √3
the tangent value of √3 in the third quadrant has the degree measure of 240 and the radian measure of 4pi/3.
Now put them together!