Judging by the symmetry of the equations, I would say that this consists of two wires, each at a distance x0 from the origin point (where x=0). They will therefore have coordinates (-x0) and (+x0). The formula then calculates the strength of the electric field at a point which is at distance x from the origin.For a long wire, the field strength at a distance d from the wire is proportional to 1/d. The distances between a point at x units from the origin and wires at +x0 and -x0. will be the difference in the coordinates, that is: x-(+x0) and x-(-x0) or to simplify, just x-x0 and x+x0.We can simply add the contributions from each wire, which is where the expression in the middle bracket comes from: 1/(x-x0) + 1/(x+x0)
