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## Homework Statement

Two particles are separated by a distance d, Particle A has charge +Q and Particle B has charge +3Q. At what distance from particle A along the line connecting particles A and B would you place a third charged particle such that no net electrostatic force acts on it ?

## Homework Equations

F = kq1q2 / r^2

## The Attempt at a Solution

Since there is no net electrostatic force on the third particle, the force from Particle A to C, and force from Particle B to C must be equal.

So I set up the equation

k(Q) / x^2 = k(3Q) / (d-x)^2

and solved for x using the quadratic formula.

I got

x = .366d

However, the answer is d/9, which is x = .111d

Can anyone help me ? Thank you