=+28. Obtain an expression for sa, the estimated standard deviation of the intercept of the least squares line.

Then use the fact that t 5 (a 2 )ysa has a t distribution with n 2 2 df to test H0:  5 0 for the data in Exercise 27 (this null hypothesis says that the population regression line passes through the origin).

Hint: When x 5 0, yn 5 a 1 b(0) 5

a, and we have a general expression for syn

.