Homework Help: Direction of electric field

1. The problem statement, all variables and given/known data

three equal and positive charges q are located equidistant from the origin as shown http://s966.photobucket.com/albums/...n=view&current=directionofanelectricfield.jpg . Is the direction of the electric field at the origin a) along x, b)along -x, c) along +y d) along -y

2. Relevant equations

The electric field is directed outward away from Q when Q is positive.

3. The attempt at a solution

Do the field lines along the x axis emerging from the charges on the x axis cancel or enhance each other at the origin?

Do I have to do vector addition on the x axis to solve this problem?

 

for the charge on the -x axis : kQ/r^3 x r_i
for the charge on the +x axis: kQ/r^3 x r_-i
for the charge on the +y axis: kQ/r^3 x r_-j

so the charges that are sitting on the x axis will cancel out. how do i write that in a more mathematical way?

 

The answer is d, along -y