分子都比分母大1,所以先整理为：原式=(x+2)/(x+1)-(x+3)/(x+2)-(x-4)/(x-3)+(x-5)/(x-4)=[1+1/(x+1)]-[1+1/(x+2)]-[1-1/(x-3)]+[1-1/(x-4)]=1+1/(x+1)-1-1/(x+2)-1+1/(x-3)+1-1/(x-4)=[1/(x+1)+1/(x-3)]-[1/...