You can put this solution on YOUR website! Y=-X NOW SUBSTITUTE -X FOR Y IN THE OTHER EQUATION
6X+6*-X=-2
6X-6X=-2
0=-2 NO UNIWUE SOLUTION.
PROOF:
Y=-X (RED LINE)
6X+6Y=-2
6Y=-6X-2
Y=-6X/6-2/6
Y=-X-1/3 (green line) (graph 300x200 pixels, x from -6 to 5, y from -10 to 10, of TWO functions y = -x and y = -x +1/3 ).