[(x - y)/xy] ÷ [(x - y)× xy/(y^2 -2xy +x^2 )]= [(x - y)/xy] ÷ [(x - y) × xy/(x-y)^2]=[(x- y)/xy] ÷ [xy/(x - y)]= [ (x - y)/xy] × [ (x - y)/xy ]= (x - y)^2/x^2y^2当 x = 3 ,y= - 1时,原式 = (3 +1)^...