a. What is a residual? b. In what sense is the regression line the straight line that "best" fits the points in a scatterplot? a. What is a residual? A. A residual is a point that has a strong effect on the regression equation. B. A residual is the amount that one variable changes when the other variable changes by exactly one unit. c. A residual is a value that is determined exactly, without any error. D. A residual is a value of y-ŷ, which is the difference between an observed value of y and a predicted value of y. b. In what sense is the regression line the straight line that "best" fits the points in a scatterplot? The regression line has the property that the of the residuals is the possible sum.