Khan Academy: Proof (Pt 2) Minimizing Squared Error to Regression Line

Video is the third of five related videos about deriving the formula for the least squares regression line. This video continues the algebraic manipulation to start deriving the formula by changing the notation to means instead of lengthy sums. It then starts showing how to use three-dimensional calculus to visualize how to minimize the sum of the errors in the formula. [9:54]