(Note: Question 1 is required. You may choose EITHER question 3. But if you work both out, you may get additional 10 points) 1. (10 points) Suppose for a standard linear model Y = X + , where E~Normal(0,022), the OLS estimator is b = (X'X)-X'Y and the GLS estimator is = (x'nx)-x'n-Y. a) (4 points) Please define the Projection matrix (P) and Residual Maker (M) and explain their uses.