6. Consider the experimental region shown in Figure 10.11, where ????1 < x1 <

1, ????1 < x2 < 1, and x2  ????2x1 ???? 2; x2  ????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.