通分：（x-1)(x-2)分之1,x的平方-2x+1分之2

若中间为加号1/［(x-1)(x-2)］+2/(x^2-2x+1)=(x-1)/［(x-1)^2(x-2)］+2(x-2)/［(x-1)^2(x-2)］
=［(x-1)+2(x-2)］/［(x-1)^2(x-2)］=(3x-5)/［(x-1)^2(x-2)］
若中间为减号1/［(x-1)(x-2)］-2/(x^2-2x+1)=(x-1)/［(x-1)^2(x-2)］-2(x-2)/［(x-1)^2(x-2)］
=［(x-1)-2(x-2)］/［(x-1)^2(x-2)］=(-x+3)/［(x-1)^2(x-2)］

1/(x-1)(x-2)=(x-1)/[(x-2)(x-1)^2]
2/(x^2-2x+1)=2/(x-1)^2=2(x-2)/[(x-2)(x-1)^2]