解方程：x²+y²+x+y=18 x²+xy+y²=19

由x²+y²+x+y=18 x²+xy+y²=19得xy=x+y+1,所以x²+2xy+y²+x+y=18+2（x+y）+2整理(x+y)^2-(x+y)-20=0即(x+y-5)(x+y+4)=0所以x+y-5=0或x+y+4=0由x+y-5=0和xy=x+y+1解得x=2,y=3或x=3,y=2由x...