visualize pi/2 as 90° on the unit circle. this has no real component, only imaginary. same for 3pi/2, or -pi/2 as shown in this equation:
[tex] - \frac{ \pi}{2} = 0 - i[/tex]
as you move around the unit circle, you'll find that 9pi/2 is the same angle as pi/2.
Thus, the rectangular coordinates are:
[tex] - \frac{9\pi}{2} = 0 - i[/tex]
