x^3m/(x^m-1)-x^2m/(x^m+1)-1/(x^m-1)+1(x^m+1)
=[x^(3m)-1]/(x^m-1)-[x^(2m) -1]/(x^m+1) (分别利用立方差和平方差可得下式)
=x^(2m) +x^m +1 -(x^m-1)
=x^(2m) +2