x-a=y-x a=2x-y
b-y=y-x b=2y-x
x/c=y/x c=x²/y
d/y=y/x d=y²/x
(a+b)-(c+d)
=(2x-y+2y-x)-(x²/y+y²/x)
=(x+y)-(x²/y+y²/x)
=(x²y+y²x-x³-y³)/(xy)
=[(x²y-x³)-(y³-y²x)]/(xy)
=[x²(y-x)-y²(y-x)]/(xy)
=[(x²-y²)(y-x)]/(xy)
=-(x-y)²(x+y)/(xy)
x>0 y>0,则xy>0 x+y>0
x≠y,则(x-y)²>0
(x-y)²(x+y)/(xy)>0
-(x-y)²(x+y)/(xy)