Where along line is electric field zero?

[Neliel06]

Homework Statement

Two charges of +4microC and +9microC are 30cm apart. Where on the line joining the charges is the electric field zero?

Homework Equations

Ep=E1+E2=0
E1=Kq1/x^2
E2=Kq2/(r-x)^2

The Attempt at a Solution

Since charges are alike, put Ep=E1-E2=0, then E1=E2
Substituted for E1 and E2
eventually leads to q1(r^2-2rx+x^2)=q2x^2

He told us to use quadratic since it's more secure, but that requires the (r^2-2rx+x^2) to be set equal to zero, which i cannot figure out how to do

 

[LowlyPion]

The way I look at it you get something like:

4/x² = 9/y²

Taking the square root of both sides yields

2/x = 3/y

That looks a little easier to deal with doesn't it?

 

[Neliel06]

Never mind, i got it. I plugged in the values for q1 and q2, distributed, subtracted the right from left, then used quadratic. Thanks for your help anyway!