1, the method of cross multiplication: the left multiplication of the cross is equal to the quadratic term coefficient, the right multiplication is equal to the constant term, and the cross multiplication is equal to the linear term coefficient.

2. Use of cross multiplication: (1) Cross multiplication is used to decompose factors. (2) Solving the quadratic equation with one variable by cross multiplication.

Advantages of cross multiplication: it is faster to solve problems with cross multiplication, which can save time and is not easy to make mistakes.