解析：若xy-x-y-4=0,那么：xy=x+y+4,xy-x-y=4(xy-1)²-2x²y-2xy²+x²+y²+6xy-2x-2y=(xy-1)²-2xy(x+y)+x²+2xy+y²+4xy-2x-2y=(xy-1)²-2xy(x+y)+(x+y)²+2(2xy-x-y)=(x...