(adsbygoogle = window.adsbygoogle || []).push({}); [SOLVED] Question about Coulomb's Law

I just solved this a problem in my text: Particle 1 of charge +1.0 uC and particle 2 of charge -3.0 uC are held at a separation L=10.0 cm on an x-axis. If particle 3 of unknown charge q3 is to be placed such that the net electrostatic force on it from 1 and 2 is zero, what must its x and y coordinates be?

Okay, I solved this using Coulomb's Law which gave me a quadratic. Thus, I got two solutions. My question is: why is one of them not valid?

I got x=.0366 and x=-.14. -.14 m is the correct answer. Why does the .0366 work? And if it does not, why did the quadratic produce it?

It may be obvious, but I am just not seeing it now.

Thanks

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# Homework Help: Question about Coulomb's Law

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