Use deMoivre's Theorem on the last form to find the 4th roots
(1) Find the "primary" root. To find the nth root of a number in a*cis(theta) form, take the nth root of a, and divide the angle theta by n.
(2) Find the other roots. The n n-th roots of a number all have the same magnitude, and they are distributed around the complex plane in intervals of (2pi)/n.
The 4th roots are at intervals of pi/2 in the complex plane. Starting with the "primary" root of 2*cis(pi/8), the four 4th roots of 16i are
