楼主所给式子,是m/(m+n)²+n/(m²-n²)-2n²/[(m+n)(m²-n²)] 如果是的话：m/(m+n)²+n/(m²-n²)-2n²/[(m+n)(m²-n²)]=m/(m+n)²+n/[(m-n)(m+n)]-2n²...