I have to convert this to polar and rectangular form:

(8 cis pi/3)(1/2 cis (-2pi/3)) = 4 cis 5pi/3, 2-2i (sq. root 3)

I just don't know how they got that answear...

I know you use the formula: rs cis (a + b) so i understand how they got 4 cis, but idk how they got the 5pi/3. And then from there i know you use r (cos theta + (sin theta)i) but i jst don't get this prob...

thanks in advance for the help