（（xx+yy）/y-2y）/（1/y-1/x）^(1/(xx-yy))

原式=[(x²+y²-2y²)/y]/[(x-y)/xy]×1/(x²-y²)
=[(x²-y²)/y]×[xy/(x-y)]×1/(x²-y²)
=xy(x²-y²)/[y(x-y)(x²-y²)]
=x/(x-y)