Suppose you have n data points (x₁, y₁) (x₂, y₂), . . , (x_n, y_n) and you wish to fit a line through the origin (y = ax) to these data using the method of least squares. Derive Equation A.1-6 (Appendix A.1) for the slope of the line by writing the expression for the vertical distance d_i from the ith data point (x_i, y_i) to the line, then writing the expression for Φ =Σd²_i, and finding by differentiation the value of a that minimizes this function.