1. The problem statement, all variables and given/known data (Lead in to question: "Assume that charges +q, -3q, 2q lie at positions -2a, 0, +2a along the x-axis respectively.") I've calculated dipole/quadrupole moments about the origin as well as the exact potential at x=+10a, however I'm confused by this next part to the question: Show that, for a 1 dimensional problem, d(1/R) / dx = -1/x² and d²(1/R) / dx² = 2/x³ where R is the distance between a lab fixed point x and an arbitrary origin x0. Can anyone suggest a method of tackling this??