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)