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## Homework Statement

Charges 4q and -q are located at the points (-2a,0,0) and (-a,0,0), respectively. Write down the potential θ(x,y) for points in the xy plane, and then use a Taylor expansion to find an approximate expression for θ near the origin, which you can quickly show is the equilibrium point. (You can set a=1 to make things simpler)

## Homework Equations

θ(x,y,s)=∫(ρ(x',y',z')dx'dy'dz')/4πεr

## The Attempt at a Solution

setting a-1, ignoring the factor of q/4πε

_{0}, the potential due to the two charges, at locations in the xy plane is θ(x,y)=(1/(sqrt((x-2)

^{2}+y

^{2})-(1/sqrt((x-1)

^{2}+y

^{2})

Have I set this equation up correctly?