Graphing a second-order model. Consider the second-order model
y = 1 + x1 - x2 + 2x12 + x22
(a) Graph the relationship between y and x1 for x2 = 0, 1, and 2.
(b) Are the graphed curves in part a first-order or second-order?
(c) How do the graphed curves in part a relate to each other?
(d) Do the independent variables x1 and x2 interact? Explain.