Question 843419
The first equation tells you that y = -x.  Substitute -x for y in the second equation.<P>
-x = 2x : add x to both sides<P>
0 = 2x + x = 3x : Divide both sides by 3.<P>
0=x :  Substitute 0 for x in the first equation.<P>
y = -0 = 0<P>
Both x and y = 0.