答：x²+y²+x+y=18,(x+y)²+(x+y)-2xy=18x²+xy+y²=19,(x+y)²-xy=19,-xy=19-(x+y)²所以：(x+y)²+(x+y)+38-2(x+y)²=18(x+y)²-(x+y)-20=0(x+y-5)(x+y+4)=0所以：x+y=5...