Consider the experimental region shown in Figure 10.9, where −1 < x1 < 1,

−1 < x2 < 1, and x2 C −2x1 − 2; x2 B −2x1 + 1.

(a) Construct a grid ±1 2 of candidate points in the (x1; x2) design region.

(b) Construct a D-optimal subset of the candidate points for tting the general quadratic model.