x+y+1=0
x³+y³=-7
x+y=-1
(x+y)(x²-xy+y²)=-7
x+y=-1
x²-xy+y²=7
x+y=-1
x²+2xy+y²-3xy=7
x+y=-1
(x+y)²-3xy=7
x+y=-1
(-1)²-3xy=7
x+y=-1
1-3xy=7
x+y=-1
-3xy=7-1
x+y=-1
3xy=-6
y=-1-x
3x(-1-x)=-6
x(-1-x)=-2
x²+x-2=0 x²+2x-x-2=0 x(x+2)-(x+2)=0 (x-1)(x+2)=0 x=1 y=-1-1=-2
x=-2 y=-1+2=1