4m/m^2-n^2 - 4/m+n = 4m/(m+n)(m-n) - 4/(m+n) =
4m-4(m-n)/(m+n)(m-n) = 4(m-1)/(m+n)
2x-y/2x+y + y/4x+2y = 2x-y/2x+y + y/2(2x+y) =
4x-y+y/2(2x=y) = 4x-y/4x+2y
x^2+y^2/x^2-y^2 - (x-y)/x+y = x^2+y^2/(x-y)(x+y) - x-y/x+y=
x^2=y^2-(x-y)(x-y)/(x-y)(x+y) = (x+y)(x-y)-x^2-2xy+y^2/(x-y)(x+y)=
x^2-y^2-x^2-2xy+y^2/(x-y)(x+y)= -2xy/(x-y)(x+y)
a+3/a-1+ a+5/2-2a
-2a-6+a+5/2-2a