The expression for the restricted coefficient vector in (6-14) may be written in the form b* = [I − CR] b + w, where w does not involve b. What is C? Show that the covariance matrix of the restricted least squares estimator is σ2 (X' X)−1 − σ2(X' X)−1 R' [R(X' X)−1R']−1 R(X' X)−1 and that this matrix may be written as Var[b |X]{[Var(b |X)]−1 − R' [Var(Rb) |X]−1R}Var[b |X].