Specific methods: when all the coefficients are integers, the coefficients of the common factor formula should take the greatest common divisor of all the coefficients; The letter takes the same letter of each item, and the index of each letter takes the lowest number; Take the same polynomial, and the polynomial has the lowest degree.

If the first term of a polynomial is negative, a "-"sign is usually put forward to make the coefficient of the first term in brackets become positive. When the "-"sign is put forward, the terms of the polynomial should be changed.

Extended data:

General steps to determine the common factor:

(1) If the first coefficient of the polynomial is negative, the sign "-"of the common factor should be extracted.

(2) Take the greatest common divisor of polynomial coefficients as the common factor.

(3) Take the product of the lowest power of the same letter (or factor) contained in each term of the polynomial as the factor of the common factor.