And then we have, almost there, home stretch, we have this over here which is plus 2mb times n times the mean of the x values. And then finally we have plus nb squared. So really in the last two, three videos, all we've done is we've simplified the expression for the sum of the squared differences from those end points to this line y equals mx plus b, right over here. So that is kind of, we're finished the hardcore algebra stage. The next stage we actually want to optimize. We actually want to optimize this. We actually want to optimize, or actually maybe a better way to talk about it, we want to minimize this expression right over here.