: Curve fitting, Correlation, and Regressions Principles of least squares, Curve fitting by the method of least squares in the form 𝑦 = 𝑎 + 𝑏𝑥 , 𝑦 = 𝑎 + 𝑏𝑥 + 𝑐𝑥2 , and 𝑦 = 𝑎𝑥 𝑏 . Correlation, Coefficient of correlation, Lines of regression, Angle between regression lines, standard error of estimate, rank correlation.