physics
posted by Megan .
Two spheres with charges of 4.00nC and 3.00nC are placed 0.500m apart. At what point between the two charges must the third charge of 2.00cN be placed so that the net electrostatic force acting on this charge is zero?

k •q1 •q3/x^2 = k •q2 •q3/(dx)^2
q1 •q3 (dx)^2 = k •q2 •q3• x^2
Solve for x 
The second line
q1 •q3 (dx)^2 = q2 •q3• x^2 
Elena, for some reason I'm getting an answer of 3
(8.00 x 10^12) x (dx)^2 = (6.00 x 10^12) x (x^2)
(dx)^2/x^2 = 7.5 x 10^1
(dx)(dx)/x^2 = 7.50 x 10^1
x^2x+0.25/x^2= 7.50 x 10^1
then I get x = 3
Can you help! I'm not sure where i am going wrong. 
q1 • (dx)^2 = q2 • x^2
4•10^9•(dx)^2 = 3•10^9•x^2
4(d^2  2•d•x + x^2) = 3•x^2,
x^2  4x + 1 = 0
x =2 ± sqrt(41) =2 ± 1.73.
x1 = 0.27 m, x2 =3.73m (falls out)