posted by Brandi .
Review Conceptual Example 7 as background for this problem. Two charges are fixed in place with a separation d. One charge is positive and has twice (n = 2) the magnitude of the other charge, which is negative. The positive charge lies to the left of the negative charge, as in the figure. Relative to the negative charge, locate the two spots on the line through the charges where the total potential is zero.
Positive distance to the left from -q:
k•2•q/(d-x) = k•q/x
Positive distance to the right of -q
k•2•q/(d+x) = k•q/x