(m-n-（4mn）/（n-m)）(m+n-（4mn）/（m+n)）=[m-n+(4mn)/(m-n)] [(m+n-(4mn)/(m+n)]=[4mn+(m-n)(m-n)] [(m+n)(m+n)-4mn] / [(m-n)(m+n)]=[(m+n)(m+n)] [(m-n)(m-n)] / [(m-n)(m+n)]=(m+n)(m-n)=m平方-n平方把m=根号...