How to Calculate the Electric Field of Two Point Charges Along the x-Axis?

[bmaia89]

Homework Statement

Here it goes.
2 pontual charges (Q>0), placed in (0,a,0) and (0,-a,0): calculate de vector E(x,0,0) along xx

Homework Equations

The Attempt at a Solution

I tried to use E=1/(4*pi*epsilon naught) * Q/r²
but when i make Q/(x ex + a ey)² and (x ex + (-a) ey)²
i don't know what to do...
(I think i have doing something wrong)

 

[rl.bhat]

but when i make Q/(x ex + a ey)2 and (x ex + (-a) ey)2
This step is not clear.
Here r^2 = x^2 + a^2.
Here E has the same magnitude but different direction. Take its components along X and y-axis and then take the resultant.

 

[bmaia89]

thanks