求极限lim(x,y)→(+∞,+∞) [(xy)/(x²+y²)]^(xy)[(xy)/(x+y)²]^(xy)≦[(xy)/(x²+y²)]^(xy)≦(xy/2xy)^(xy)左边=(x,y)→(+∞,+∞) lim[(xy)/(x+y)²]^(xy)=(x,y)→(+∞,+∞) lim[(xy)/(...