the complex number -4 has a degree of 180 degrees. that means that the degrees of the solutions are going to be 180/4=45, 180/4+360/4=135, 180/4+360/4+360/4=225, and 180/4+360/4+360/4+360/4=315.
The magnitude of -4 is obviously 4, so the magnitude of the solutions are going to be 4^(1/4) = sqrt(2)
Therefore, the solutions in polar form are: √2(cos(45)+isin(45)),√2(cos(135)+isin(135)),√2(cos(225)+isin(225)),√2(cos(315)+isin(315))
Simplifying gives −1−i,−1+i,1−i,1+i
(notice that I gave a general way to solve this problem, but obviously, for this problem, you could factor it and solve it in a quicker way.)