Hoặc
a) 1x−2−1x+1;
a) 1x−2−1x+1=x+1(x−2)(x+1)−x−2(x−2)(x+1)
=x+1−(x−2)(x−2)(x+1)=x+1−x+2(x−2)(x+1)=3(x−2)(x+1);