x+2y=1
xy=-1
x=1-2y
(1-2y)y=-1
y-2y²=-1
2y²-y-1=0
2y²-2y+y-1=0
2y(y-1)+1(y-1)=0
(2y+1)(y-1)=0
y=-1/2 ∨ y=1
x=1-2*(-1/2) ∨ x=1-2*1
x=1+1 ∨ x=-1
x=2 ∨ x=-1
(2,-1/2) , (-1,1)
x+2y=1
xy=-1
x=1-2y
xy=-1
(1-2y)y=-1
y-2y²=-1
2y²-y-1=0
2y²-2y+y-1=0
2y(y-1)+1(y-1)=0
(2y+1)(y-1)=0
y=-1/2 ∨ y=1
x=1-2*(-1/2) ∨ x=1-2*1
x=1+1 ∨ x=-1
x=2 ∨ x=-1
(2,-1/2) , (-1,1)