Hi,

I need to find all roots to the equation $\displaystyle z^4=-16i$

This is what i tried:

$\displaystyle |-16|^{1/4}=2$

And the angle of -16i is 270 degrees or $\displaystyle \frac{3\pi}{2}$

All the roots are on the form $\displaystyle |z|^{1/n}\cdot cos\frac{\theta}{n}+isin\frac{\theta}{n}$

So the first root should be $\displaystyle 2\bigg(cos(\frac{3\pi}{8})+isin(\frac{3\pi}{8})\bi gg)$

But it's just not correct.