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)
The Attempt at a Solution
setting a-1, ignoring the factor of q/4πε0, the potential due to the two charges, at locations in the xy plane is θ(x,y)=(1/(sqrt((x-2)2+y2)-(1/sqrt((x-1)2+y2)
Have I set this equation up correctly?