98. Consider the special case y  b0  b1x 

e, so k  1 and X consists of a column of 1 s and a column of the values x1, . . . , xn of x.

a. Write the normal equations in matrix form, and solve by inverting XX. Hint: If ad  bc, then Check your answers against those in Section 12.2.

b. Use the inverse of XX to obtain expressions for the variances of the coef cients, and check your answers against the results given in Sections 12.3 and 12.4 ( is the predicted value corresponding to x*  0).

c. Compare the predictions from this model with the predictions from the model of Exercise 92.

Comparing other aspects of the two models, discuss similarities and differences. Mention, in particular, the hat matrix, the predicted values, and the residuals.