在多项式的因式分解中,我们最感困难的,是含有两个或两个以上字母的多项式的因式分解。这种多项式的字母排列,有时好象“杂乱无章”,无法入手。这时,我们只要恰当地选取一个字母作“主变量”,把其余字母及常数作“常量”,变形为含这个主变量的“二次三项式”,即可用“十字相乘法”或提取公因式法来分解。 In the factorization of polynomials, what we find most difficult is the factorization of polynomials that contain two or more letters. The polynomial alphabetical arrangement sometimes seems to be “disorderly” and cannot be started. At this time, we only need to properly select one letter as the “subject variable” and change the remaining letters and constants as “constants” to the “secondary trinomial” containing this host variable. Then we can use “cross-multiplication” or Extract the common factor method to decompose.