Please see question as below. I attached a picture.

4. Suppose yi = Bo+ Bici te for i = 1,..., n, where $1, ...; In are known constants and E(c) =0, i=1, ...,n Cov ( 6, 6; ) = "? ifi=] ij = 1, . .. .n. if i # j' Let Bo and 3, be the ordinary least squares estimates for 3, and B, and define E = yi - Bo - BIti, i= 1, ...,n. (a) Prove that the vector of e's is orthogonal to the design. That is, prove Ed = Can =0. (b) Let yi = Pot Bit, = n->