Help figuring out Electric Potential

1. Jan 28, 2010

Dudemanword

1. The problem statement, all variables and given/known data
Three charges are laid out in a Cartesian Plane:
+q: (0,a)
-q: (0,0)
+q: (0,-a)

There is some point p located on the x-axis in the positive x direction

Show that the points where the Electric potential is 0 is x= +/- a/sqrt(3)

2. Relevant equations

I believe I am to use
\begin{flalign*} V = \frac{1}{4 \pi \epsilon_0} \ \frac{q}{r}\\ \end{flalign*}
because they are point charges

3. The attempt at a solution
I created right triangles using "P" as a point to start pythagorizing( is that a word?). Eventually I simplified it to q/(x(sqrt(a^2+x^2))
No idea how to get it to +/- a/sqrt(3)

Last edited: Jan 28, 2010