11.2 Understanding the fitted regression line. The fitted regression equation for a multiple regression is

  1. (a) If x1 = 4 and x2 = 2, what is the predicted value of y?

  2. (b) For the answer to part (a) to be valid, is it necessary that the values x1 = 4 and x2 = 2 correspond to a case in the data set? Explain why or why not.

  3. (c) If you hold x1 at a fixed value, what is the effect of an increase of three units of x2 on the predicted value of y?