Hi

How would i do the following question:

Find the roots of the equation: $\displaystyle z^4-1$

This is what i have done:

$\displaystyle z^4 = -1 $

$\displaystyle z^4 = cis(\frac{\pi}{4}) $, $\displaystyle cis(\frac{5\pi}{4})$, $\displaystyle cis(\frac{9\pi}{4})$, $\displaystyle cis(\frac{13\pi}{4}$

$\displaystyle z^4 = cis(\frac{\pi}{16}) $, $\displaystyle cis(\frac{5\pi}{16})$, $\displaystyle cis(\frac{9\pi}{16})$, $\displaystyle cis(\frac{13\pi}{16}$

P.S