在分解因式时,有时遇到的多项式中,不止一个字母,若认定其中某一个字母为主元,按降幂排列,便会发现有公因式可提或可利用公式,给分解带来方便,请看下面的例子.例1 分解因式 bc(b+c)+ac(c-a)-ab(a+b).解选取 b 为主元,整理,得原式=(c-a)b~2+(c~2-a~2)b+ac(c-a)=(c-a)[b~2+(c+a)b+ac] When decomposing factors, there are more than one letter in a polynomial that is sometimes encountered. If one of the polynomials is determined to be the primary element and is arranged in a descending power, it can be found that there is a public factor formula or formula that can be used to bring about decomposition. Conveniently, see the following example. Example 1 Decomposition factor bc(b+c)+ac(ca)-ab(a+b). Solution b is the main element, sorting, get the original type = (ca)b~ 2+(c~2-a~2)b+ac(ca)=(ca)[b~2+(c+a)b+ac]