Use the result of part (b) of Exercise 20 to show that
is a value of a random variable having the standard normal distribution. Also, use the first part of Theorem 3 and the fact that 
are independent to show that
is a value of a random variable having the t distribution with n - 2 degrees of freedom.
Exercise 20
Under the assumptions of normal regression analysis, show that
(a) the least squares estimate of α in Theorem 2 can be written in the form
(b) 
has a normal distribution with
Theorem 2
