1. The problem statement, all variables and given/known data A circular ring of wire of radius r0 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-axis direction, E, at the point given by E=kx/((x^2 +r0^2)^(3/2)) for k>0 at what point on the x-axis is greatest? least? 2. Relevant equations 3. The attempt at a solution so the only thing i could really think of to do is take the derivative. the circle itself isn't changing so I assumed r0 is a constant as well as k. [itex]E'=(k(x^2 + r0^2)^(3/2) - 3kx^2√(x^2 +r0^2))/((x^2 +r0^2)^(3/2))[/itex] after this i find the critical points 0=(k(x^2 + r0^2)^(3/2) - 3kx^2√(x^2 +r0^2))/((x^2 +r0^2)^(3/2)) 0=(x^2 +r0^2)^(3/2) -3x^2√(x^2+r0^2) im not sure what do here. I feel like I should have solved for r0 in terms of x, but im not sure.