2. Factorization skills:

① The left side of the equation must be a polynomial;

② The result of factorization must be expressed in the form of product;

③ Each factor must be an algebraic expression, and the degree of each factor must be lower than that of the original polynomial;

④ Factorization factors must be decomposed until each polynomial factor can no longer be decomposed.

Note: Find the common factor before decomposing the factor, and consider the coefficient and factor before determining the common factor.

3. Basic steps of common factor method:

(1) Find the common factor;

(2) Take the common factor and determine another factor:

① The first step of finding the common factor is to determine the coefficient first and then the letters according to the method of determining the common factor;

(2) The second step is to mention the common factor and determine another factor, and pay attention to determining another factor.

(3) After extracting the common factor, the number of terms of another factor is the same as that of the original polynomial.