If you had a system that led to an impossible equation, such as $\displaystyle{0}={1}\usepackage{cmbright}\Huge\$ , then there would be no solution. If you multiply the second equation by $\displaystyle-{6}\usepackage{cmbright}\Huge\$ and add it to the first equation, then you end up with $\displaystyle{0}={0}\usepackage{cmbright}\Huge\$ . This is true regardless of the value of x or y.