Here's how far I got with this problem. Not sure how to go on...
r = √ [ (-3)^2 + (3√3)^2 ] = √ [ 9 + 27] = √36 = 6
θ = arctan (3√ 3 / -3) = arctan (-√ 3) = -pi/ 3 + pi = 2pi/3
z = 6 cis (2pi/3)
Thanks so much CPhill!
