[1/(x^2-2x)-1/(x^2-4x+4)]/[2/(x^2-2x)] =[1/x(x-2)-1/(x-2)^2]*[x(x-2)/2] =1/2-x/2(x-2) 当x=1时,原式=1/2-1/[2*(1-2)]=1/2+1/2=1
