The handout for work in class is here.

And here are three files (pdf, Mathematica notebook (nb) (if you have Mathematica), and a supposedly interactive Mathematica file (cdf)) showing how one might convince Mathematica to use calculus to solve the least squares problem. here for nb, here for cdf, here for pdf.

The source for both handouts is (for now without my comments) here.

The commented handout is here.