Trouble with optimization

A circular ring of wire of radius r_0 lies in a plane perpendicular to the x-axis and is centered at the origin. The ring has a positive electric charge spread uniformly over it. The electric field in the x-direction, E, at the point x on the axis is given by the following formula where k > 0.

E=(kx)/(x^2+(r_0)^2)^(3/2)

At what point on the x-axis is the field greatest?

At what point on the x-axis is the field least?

This problem is just getting very messy and I am sure that is not right, any help is appreciated.