In the model (9.17), show that OLS consistently estimates a and ( if a1. is uncorrelated with

Question:

In the model (9.17), show that OLS consistently estimates a and ( if a1. is uncorrelated with xi. and bi. is uncorrelated with xi. and xi2, which are weaker assumptions than (9.19). [Write the equation as in (9.18) and recall from Chapter 5 that sufficient for consistency of OLS for the intercept and slope is E(ui) = 0 and Cov(xi, ui) = 0.]