Cross factorization: first divide the quadratic term coefficient into two products, then divide the constant term into two products, and then the cross product is equal to the linear term coefficient.

1, common factor extraction method.

2. Formula method (square difference formula and complete square formula).

For example: matching method and crossover method.

(x+2y)(2x- 1 1y)= 2 x2-7xy-22 y2 .

(x-3)(2x+ 1)=2x2-5x-3 .

(2y-3)(- 1 1y+ 1)=-22 y2+35y-3 .

This is called double cross multiplication.

Method formula of cross multiplication:

Cross left multiplication equals quadratic coefficient, right multiplication equals constant term, and cross multiplication plus equals linear coefficient. ?

The use of cross multiplication:

(1) uses cross multiplication to decompose the factor.

(2) Solving the quadratic equation with one variable by cross multiplication.

Advantages of cross multiplication:

Using cross multiplication to solve problems is faster, can save time, and the calculation is not large, so it is not easy to make mistakes.