- #1

raintrek

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## Homework Statement

(Lead into 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??