imagine a rectangle of width 2l and height l, better yet draw the rectangle on a piece of paper. point charges sit at each corner of the rectangle, specifically: charge q>0 sits at the upper-left corner charge -2q at the lower-left corner charge -q at the upper-right corner charge 2q at the lower-right corner now consider these three locations: a is the middle of the left edge of the rectangle b is the middle of the lower edge of the rectangle c is the middle of the right edge of the rectangle rank the potentials at points a, b, and c from greatest to least (positive potentials should also be ranked above negative potentials).
