x²-xy-3x=0
x(x-y-3)=0
x=0,x=y+3
x=0
代入x²+y+1=0
y=-1
x=y+3
代入x²+y+1=0
y²+7y+10=0
(y+2)(y+5)=0
y=-2,y=-5
x=y+3
所以
x=0,y=-1
x=1,y=-2
x=-2,y=-5