Solving a system and ending up with the equations $\displaystyle{x}={0}\usepackage{cmbright}\Huge\$ and $\displaystyle{y}={0}\usepackage{cmbright}\Huge\$ means that the solution is (0, 0). This is very different from ending up with the equation $\displaystyle{0}={0}\usepackage{cmbright}\Huge\$ . When a system leads to an equation such as $\displaystyle{0}={0}\usepackage{cmbright}\Huge\$ , which is true regardless of the value of x or y, there are an infinite number of solutions.