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Member advised to use the homework template for posts in the homework sections of PF.

**and two -q charges aligned along the x axis as follows...**

-q__________q__________-q <--- the space between them being d

a) Suppose the +q charge is displaced perpendicularly by a small vertical distance dy. What is the total force F acting on it? Taylor expand your answer to leading order in dy

-q__________q__________-q <--- the space between them being d

a) Suppose the +q charge is displaced perpendicularly by a small vertical distance dy. What is the total force F acting on it? Taylor expand your answer to leading order in dy

**b) Next suppose instead the +q charge is displaced along the x axis by a small dx distance. What is the force acting on it?**

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So for a) I'm kind of stuck at the Taylor expansion on the force.

F = (q)(-q)/4piε

_{0}d

^{2}yhat + (q)(-q)/4piε

_{0}d

^{2}

where d= sqrt(x^2+dy^2)

I'm at a point where I'm trying to simplify something but feel that I"m doing something wrong in the math

Same for b)

Thanks!