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undrcvrbro

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## Homework Statement

A 1.4*10-9 C charge is on the x-axis at x = -2.0 m, a 7.0*10-9 C charge is on the x-axis at x = 2.5 m. Find the net force exerted on a 4.0*10-9 C charge located at the origin.

## Homework Equations

F=k(q1*q2) / (r^2)

k= 9*10^9

## The Attempt at a Solution

I simply took the difference of the two Forces existing between the central charge and each end of the axis.

I took:

F= (9*10^9)(1.4*10^-9)(4.0*10^-9) / (2)^2

and then subtracted it from:

F= (9*10^9)(7.0*10^-9)(4.0*10^-9) / (2.5)^2

But that obviously isn't correct, because Web assign gave me a big red X when I plugged the answer in. Any help is greatly appreciated!