When factorizing some polynomials, it is necessary to restore those items that are merged or offset each other, that is, to split one term in a polynomial into two or more terms, or to only satisfy the addition of two opposite terms. The former is called a split item. The latter is called addition. The purpose of item splitting and addition is to decompose polynomial factors by grouping decomposition. Let's take an example: factorization factor: x3-9x+8 solution 1 decomposes the constant term 8 into-1+9. Original formula = x3-9x- 1+9 = (x3-65438)