A chain with uniform mass density per unit length hangs between two supports located at the same

Question:

A chain with uniform mass density per unit length hangs between two supports located at the same height, a distance 2d apart (see Fig.). What should the length of the chain be so that the magnitude of the force at the supports is minimized? You may use the fact that a hanging chain takes the form, y(x) = (1/a) cosh(ax). You will eventually need to solve an equationnumerically.