Show that the second term on the right in (7.17) is zero if X is the incidence matrix for

(i) an unbalanced one-way layout

(ii) a randomized blocks design (two-way design) with equal numbers of replications per cell.

(iii) a Latin square design.

Show that the second term is not zero if X is the model matrix for an ordinary linear regression model in which more than two x-values are observed.

 P=869