x²y²+x²+y²+1=4xy(x²y²-2xy+1)+(x²+y²-2xy)=0(xy-1)²+(x-y)²=0因为(xy-1)²≥0 (x-y)≥0所以xy-1=0 ① x-y=0 ②由②得x=y,代入①得y²-1=0,解得y=1或-1...