X^2/(x^2+2xy+y^2) : (x/(x+y) - xy/(y^2-x^2))=
1) (x/(x+y) - xy/(y^2-x^2)) = (x/(x+y) - xy/((y-x)(y+x))= (x(y-x)-xy)/((x-y)(x+y))= (xy-x^2-xy)/((y-x)(y+x)) = -x^2/((y-x)(y+x))
2) x^2/(x^2+2xy+y^2) : (-x^2)/((y-x)(y+x)) = x^2/(x^2+2xy+y^2) * ((y-x)(y+x))/(-x^2) = x^2((y-x)(y+x))/((x^2+2xy+y^2)(-x^2)) = -(y-x)/(x+y)= (x-y)/(x+y)