Suppose the true relationship between E(y) and the quantitative independent variables x1 and x2 is given by the model below.

E1y2 = -5 + x1 + 3x2 - 3x1 x2

a. Describe the corresponding three-dimensional response surface.

b. Plot the linear relationship between y and x2 for x1 = 0, 1, 2, where 0 … x2 … 5. Choose the correct graph below.

c. Explain why the lines you plotted in part b are not parallel.

d. Use the lines you plotted in part b to explain how changes in the settings of x1 and x2 affect E(y).

e. Use your graph from part b to determine how much E(y) changes when x1 is changed from 1 to 2 and x2 is simultaneously changed from 1 to 0.