First of all, you'll need a 2, somewhere.
|z| = cis(x/3) really doesn't make quite enough sense. It is as if you ALMOST know where you are going.
Just apply the theorem from DeMoivre.
for k = 0, 1, 2
k = 0 leads to
k = 1 leads to
k = 2 leads to
One for free. You show us the next one.