? In order to minimize the sum of squares of residuals, the sum of squares of residuals ∑ei2 takes the derivative of the regression coefficient and makes it 0, then the above formula can be obtained, that is ∑eixi=0.

Econometrics is a subject that combines economic theory with mathematical statistics and makes quantitative analysis with actual economic data.

The main contents include theoretical econometrics and applied econometrics. Theoretical econometrics mainly studies how to use, transform and develop mathematical statistics methods to make them a special method to measure stochastic economic relations.

Applied econometrics is to study the practicability of economic mathematical models or explore empirical economic laws with econometric methods under the guidance of certain economic theories and based on statistical data reflecting facts.