y=1/(x-1)(x-2)=1/(x-2)-1/(x-1)=-0.5/(1-x/2)+1/(1-x)=-0.5[1+x/2+x^2/4+x^3/8+...]+[1+x+x^2+x^3+...]=(1/2)+(3/4)x+(7/8)x^2+...+(1-1/2^(n+1))x^n+...收敛域为|x|