(x+2)/(x+1)-(x+3)/(x+2)=(x+4)/(x+3)-(x+5)/(x+4)[(x+1+1)/(x+1)]-[(x+2+1)/(x+2)]=[(x+3+1)/(x+3)]-[(x+4+1)/(x+4)]1/(x+1)-1/(x+2)=1/(x+3)-1/(x+4)1/[（x+1）(x+2)]=1/[（x+3）(x+4)]（x+1）(x+2)=（x+3）(x+4）...