(1)m+2n/n-m+n/m-n
=(m+2n-n)/(n-m)
=(m+n)/(n-m)
(2)m^2-m/m^2-1-m-1/m+1
=m(m-1)/[(m-1)(m+1)]-(m-1)/(m+1)
=m/(m+1)-(m-1)/(m+1)
=(m-m+1)/(m+1)
=1/(m+1)