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