y=6-2x
xy+x=3
x(6-2x)+x=3
6x-2x^2+x=3
2x^2-5x=3
2x^2-5x-3=0
(2x+1)(x-3)=0
x=-1 or x=+3
x = 3 (y = 0) is certainly a solution, but x = -1 isn't!
Always pays to put your solutions back into the original equations to check.
(The other solution is x = 1/2, y = 5)
.
