Yes, it means plotting another set of points with y being negative. I plotted both sets of these points on a graph. The original set of points is a line with a negative slope that crosses the x axis at 3. The second set of points, when y is negated, is a line with a positive slope and it also crosses the x axis at 3. The question is, what inference can you make about the result of the location of a point when the sign of the y- coordinate is changed? I don't know what else to say about it, other than the slope of it changes from being negative to being positive.