2) 4m/(m-n)(m+n) - 4/m+n = (4m-4(m-n)) / (m-n)(m+n)= (4m-4m+4n)/(m-n)(m+n)= 4n/(m-n)(m+n)
4) (x^2+y^2)/(x+y)(x-y) - (x-y)^2/(x+y)(x-y) = (x^2 + y^2 -x^2+xy+xy-y^2)/(x+y)(x-y)= 2xy/(x+y)(x-y)
6) 1/ 2(m-2) + m/(2-m)(2+m) = 1/ -2(2-m) + m/(2-m)(2+m) = (2 + m - 2m)/(-2)(2-m)(2+m) = 1/ -2(2-m) = 1/ -4+2m