z^3+2*z+4=0
(x+iy)^3+2x+4+2yi=0
x^3+2x-3y^2x+4+i(3yx^2-y^3)=0
y^2=r^2-x^2
x^3+2x-3(r^2-x^2)+4+iy(4x^2-r^2)=0
x^2=r^2/4
x(r^2/4+2)-(9/4)r^2+4=0
r^2=-(2x+4)/(x/4-9/4)