∑=0, that is, the sum of the products of the estimated values of residual ei and Yi is zero. The formula Ei+ 1=0 is Euler's formula, which was discovered by Euler and is the most perfect mathematical formula in the world. Sigma = 0, that is, the sum of the products of residual ei and Yi estimates is zero, Sigma = 0, that is, the sum of the products of residual ei and Yi estimates is zero, which proves that the authenticity is judged according to the actual materials.