Note Set 15c: Let's fit a line using the Normal Equation goodness

We deploy the Normal Equation for the simple and essential activity of fitting a straight line through a set of paired data points. Of course, it's all about $\mathbf{A}\vec{x}=\vec{b}$. However many points we start with, we end up with a super simple 2 by 2 system.
Best consumed by 2016/10/12