Consider the model
y = β0 + 1x1 + 2x1 2 + 3x2 + 4x3 + 5 x1x2
+ 6x1x3 + 7 x12 x2 + 8 x12 x3 + (
Where x1 is a quantitative variable and

The resulting least squares prediction equation is

a. What is the equation of the response curve for E(y) when x2 = 0 and x3 = 0? When x2 = 1 and x3 = 0? When x2 = 0 and x3 = 1?
b. On the same graph, plot the least squares prediction equation associated with level 1, level 2, and level 3.

1 if level 3 (1 if level 2 lo otherwise lo otherwise X3 = = 48.8 3.4x1 + .07x 2.4x2 7.5x3 + 3.7x,x2 + 2.7x1x3 .02x}x2 .04x}x3