Where the total electric field is equal to zero?

[barrett]

Homework Statement

Two point charges of -2.5 µC and 6.0 µC lying along the x-axis are 1.0 m apart. Locate the point (other than infinity) at which the total electric field is zero.

Homework Equations

I was thinking: E=F/q
and
F=K (Q x q)/d^2
But I'm not quite sure how to use them.

The Attempt at a Solution

Using the second equation I found F to be -.135. But I don't think that's right, and then when plugging that into the E=F/q. E would have to be zero, since I'm trying to find where the total electric field is zero? Then there's no solutions other than infinity, are there? And what exactly is q in the first equation. I really have no idea what's going on here.

 

[qspeechc]

If the electric field is zero, is it the case that the force is also zero? So find the point(s) where the net electric force or field is zero.

 

[barrett]

I found an example online and I think I substituted the right numbers in for this problem, is this how it would be solved? (I didn't understand the equation below and where it came from: KQ/x²-2.4KQ/(x+1.00)²)

Enet=Esub1 + Esub2 = KQ/x²-2.4KQ/(x+1.00)²
KQ/x²-2.4KQ/(x+1.00)²

The Ks and Qs cancel out leaving:
1/x² = 2.4/(x+1.00)²

And then get it into a quadratic:
1.4x² - 2x -1=0

And find it to be 1.82 m to the left of charge Q. I ignored the other root, -.39m because that would be between the two charges where the fields cannot cancel out.
Am I on the right track?