Add x to the <em>first equation</em> to put it in standard form:
... x + y = 3
Divide the <em>second equation</em> by the common factor of all terms, 2, to put it in standard form:
... x + y = 3
These two equations describe the same line. Every point on the line is a solution to both equations, so there are infinitely many solutions. (We say these equations are "dependent.")
