[tex] \left \{ {{2x=2y+2\ \ \ \ \ \ \ \ \ \ \ \ \ } \atop {2y=2x-2\ \ \ |subtract\ 2x}} \right.\\\\ \left \{ {{2x=2y+2\ \ \ \ \ \ \ \ \ \ \ \ \ \ } \atop {0=2x-2y-2\ \ \ |subtract\ 2x}} \right.\\\\ \left \{ {{2x=2y+2} \atop {-2x=-2y-2}}\\ \right.\\+-------Addition\ method\\\\
0=0\\\\ There\ are\ infinitely\ many\ solutions\\
This\ is\ identity.
[/tex]
