4xy-(x+y)^2/xy(x+y)(x-y)÷x^2+xy-2y^2/x^2y+2xy^2
=(4xy-x²-2xy-y²)/[xy(x+y)(x-y)]÷[(x-y)(x+2y)]/[xy(x+2y)]
=-(x-y)²/[xy(x+y)(x-y)]÷(x-y)/xy
=-1/(x+y)