(1)1/2x-2,=(x-1)/2(x-1)^2
1/(x-1)的二次方=2/2(x-1)^2
(2)1/(x-1)的二次方=x^2(x-2)/x^2(x-1)^2(x-2),
2/x的二次方=2(x-1)^2(x-2)/x^2(x-1)^2(x-2),
3/(x-1)(x-2)=3x^2(x-1)/x^2(x-1)^2(x-2)