（1）2xy(x-y)/[(x+y)²(x-y)]与x(x+y)/[(x+y)²(x-y)](2) (x²-y²)/2(x+y)²与2xy/2(x+y)²(3)2mn(2m+3)/[4(m²-1)(2m+3)]与(2m-3)(4m²-4)/[4(m²-1)(2m+3)]