Please help with simple linear regression!

[Tommy1005]

Heres the problem, i had to post a screen shot of it because of all the algebraic symbols..

http://img190.imageshack.us/img190/5591/problemvp.jpg

And the Linear Regression model given in 2.4 is y = B1 + B2x + e

(those B's are beta's, just like in the link above)

[Zanetti]

you can prove this geometrically. Let C(X) be the column space of the matrix [1,X] consisting of 2 columns (1st column is n-dimensional vector where all the entries are 1, and 2nd column is your n-dimensional vector X, so the matrix is of size n by 2) now yhat - ybar belongs to C(X) and ehat is orthogonal to C(X) so the sum in the question is nothing but the dot product between them so it equals 0 since they're orthogonal. Hope this helps!

[Tommy1005]

holy cow thats confusing, anyway you can show it by hand?