You need to use a theorem know as De' Moivre'sOriginally Posted by c_323_h
You need to express
Now, express in trigonomteric form,
By De Moivre's Theorem,
But, this is only one solution there are 3 more (because of the degree). In this case, we divide, by the degree, (4) to get, and each other solution is added by
If you want you can add to your first solution to get,
The beauty of the second result is that it is very easy to see, that each one is divided by 8 and the numerator is increasing by 4.