分子展开合并(ax1+1)(x2+2)-(ax2+1)(x1+2)=ax1x2+2ax1+x2+2-ax1x2-2ax2-x1-2=2ax1-2ax2+x2-x1=2a(x1-x2)+x2-x1=(x1-x2)(2a-1)
把分子的多项式打开后再进行因式分解即可~
