http://i.imgur.com/DkYMylb.png, probably easier to understand than me trying to type it out. so far I tried exapanding the (y_i - y(x_i))^2 and and then subbing in y_i = ax + b. This gives me part of the answer but i'm not sure if it's legal. I'm generally struggling to find a workable relationship between yi, y and y(bar), same for x. If nothing else, I could use some clarification as to what the y is (y_i - y(x_i))^2. I thought maybe it was like f(x) but if that's not the case, what would it be if not y_i? Thanks for your help.