What is the "999 formula"

"99 multiplication table" is a mathematical formula that primary school students can use flexibly, and it has been used all over the world for more than two thousand years. Zhang Jing, a teacher of Acheng No.8 Middle School in Harbin, invented the formula of "addition, subtraction and Divison" after years of painstaking research. "Two-three get six" and "three-three get nine" are our random formulas, and children have been learning to use "small ninety-nine" for operations since primary school. Zhang Jing told reporters that when he studied multiplication formula in elementary school, he thought, since multiplication has a formula, then addition, subtraction and division must also have a formula. When he grew up, the idea stayed in his mind. By chance, Zhang Jing found that the complex relationship between numbers is not a simple number code, and then obtained the operation rules of addition, subtraction and division by calculation. Later, after sorting out by my son Zhang Xuguang, I found that the logical relationship of addition, subtraction and division and the arrangement of numbers are completely consistent with the multiplication formula. Thanks to the efforts of father and son, the formulas of addition, subtraction and division came out one after another. Zhang Jing called them "999 formula" together with multiplication formula. include