[(x√y-y√x)/(x√y+y√x)]-[(y√x+x√y)/(y√x-x√y)]
=[(√x-√y)/(√x+√y)]-[(√y+√x)/(√y-√x)] 这一步是两分式分子分母分别同除以√(xy)
=[(√x-√y)²/(x-y)]-[(√x+√y)²/(y-x)]
=[(√x-√y)²+(√x+√y)²]/(x-y)
=(2x+2y)/(x-y)
=2(x+y)/(x-y)