Question

Consider point charges + Q and +9Q, which are separated by 12 meters. At what point, on a line between the two charges, would it be possible that the electric field would be zero.
A. There is no such point possible
B. 9 meters from the +Q charge
C. 9 meters from the +9 Q charge
D. 1 meter from the +Q charge
E. None of the above
Show work

Answer 1

Let x be the distance from the Q charge.

E=0=kQ/x^2 -k9Q/(12-x^2

or

9x^2=144-24x+x^2
or

8x^2+24x-144=0

Use the quadratic equation.

Answer 2

A. There is no such point possible
B. 9 meters from the +Q charge
C. 9 meters from the +9 Q charge
D. 1 meter from the +Q charge
E. None of the above

I don't understand how you use the quadratic formula to solve for this problem
getting x = 1.5 + -3.9686i...