x=y+7
xy=-12
(y+7)y=-12
y²+7y=-12
y²+7y+12=0
y²+3y+4y+12=0
y(y+3)+4(y+3)=0
(y+4)(y+3)=0
y=-4 ∨ y=-3
x=-4+7
x=3
x=-3+7
x=4
(3,-4),(4,-3)
x=y+7
xy=-12
(y+7)y=-12
y²+7y=-12
y²+7y+12=0
y²+3y+4y+12=0
y(y+3)+4(y+3)=0
(y+4)(y+3)=0
y=-4 ∨ y=-3
x=-4+7
x=3
x=-3+7
x=4
(3,-4),(4,-3)