[x-y/2x+2y]-[x²+y²/x²-y²]
=（x-y)/2(x+y)-(x²+y²)/(x+y)(x-y)
=[（x-y)（x-y)-2(x²+y²)]/2(x+y)(x-y)
=- (x+y)²/2(x+y)(x-y)
=(x+y)/2(y-x)