Electric fields two point charges

[mussgo]

i just need to get this question over with
i tried and tried but i couldn't get the right answer plss anyone u.u

1. Homework Statement

point charges q1 = -6q and q2 = +3q are separated by distance d. Locate the point (measured from the origin at q1) at which the electric field due to the two charges is zero.
<img src=http://www.webassign.net/hrw/23_30.gif>



2. Homework Equations
E=kQ/x^2


3. The Attempt at a Solution

well i did 0= E1+E2

i got this

0 = 3kQ/x^2 - 6kQ/(x+d)^2

6kQ/(x+d)^2 = 3kQ/x^2

cross multiplied

2x^2 = x^2 + 2dx + d^2

x^2 - 2dx - d^2 = 0

and then i did quadratic formula and got d-+d(sqrt2)
like 2.414d and .414 but as i put them in the webassign i got em wrong
can anyone help or tell what i did wrong or any feedback would be apreciated u.u

 

[Ronnin]

There is only one point where the charges cancel each other out. It is one of the two you have calculated for, but only one has the E field vectors pointing opposite directions, which give a net charge of zero.

 

[mussgo]

but something must be wrong because like i said earlier
the webassign says its wrong :S u___U

 

[Shooting Star]

> point charges q1 = -6q and q2 = +3q are separated by distance d. Locate the point (measured from the origin at q1) at which the electric field due to the two charges is zero.

> got this

0 = 3kQ/x^2 - 6kQ/(x+d)^2

You origin is given at q1 = 6q, but you are measuring x from the other charge.

 

[mussgo]

true :O
im going to try it
and see what comes out :O