p
$\displaystyle \frac{z-1}{z}=-\frac{i}{1-i}=1/2(1+i);\quad z=1-i$
$\displaystyle \sqrt{1/2(1+i)}=\frac{1}{\sqrt{2}}\sqrt{1+i}$
$\displaystyle =\frac{1}{\sqrt{2}} 2^{1/4}e^{i/2(\Theta+2k\pi)}$
then:
$\displaystyle r_1=2^{-1/4}e^{\pi i/8}$
$\displaystyle r_2=2^{-1/4}e^{9\pi i/8}$
Now you can separate out the real and imaginary components using Euler's formula.
Ok, sorry. I made a mistake. It's:
$\displaystyle -\frac{i}{1-i}\left(\frac{1+i}{1+i}\right)=-\frac{i(1+i)}{2}=\frac{1-i}{2}$
Also, Euler's Formula is $\displaystyle e^{a+ix}=e^a(\cos(x)+i\sin(x))$ and that's how you separate the real and imaginary components out if the number is in exponential form.