The lines of electric force of two opposite charges of the same strength at (?? 1, 0) and (1, 0) are the circles through (?? 1, 0) and (1, 0). Show that these circles are given by x2 + (y ?? c)2 = 1 + c2. Show that the equipotential lines (orthogonal trajectories of those circles) are the circles given by (x + c*)c2 + y2 = c*2 ?? 1 (dashed in Fig.25)