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## Homework Statement

Consider the figure below, we need to find the charge on [itex]Q_0[/itex], both charges Q are negative. It is given that the net charge on [itex]Q_A[/itex] is zero.

The figure of the problem is attached.

## The Attempt at a Solution

I understand how to get the solution except for one part. I'm just going to write [itex]F_x[/itex] and [itex]F_y[/itex] below to denote the forces components as the numbers aren't relevant (I don't think?) for my question.

I understand that we can discard the constant [itex] 1/4\pi\epsilon_0[/itex] or

*k*whichever is preferred and that we can get rid of the [itex]a^2[/itex] terms in denominators when taking the radius and likewise for sin/cos for the respective components.

The solution is [itex] Q_0 Q/8 = \sqrt {F_x^2 + F_y^2}[/itex].

Now the solution is obtained by [itex]Q_0 = 8 * \sqrt {F_x^2 + F_y^2} [/itex]

Why is Q discarded here? I just don't see where it goes mathematically.. it just kind of "disappears". Is it discarded because it is stated that the net force caused by this charge is negligible?

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