If you end up with an equation that is always true, such as $\displaystyle{x}={x}\usepackage{cmbright}\Huge\$ or $\displaystyle{0}={0}\usepackage{cmbright}\Huge\$ , then there are an infinite number of solutions. However, if you multiply the second equation by $\displaystyle-{7}\usepackage{cmbright}\Huge\$ and add it to the first equation, you will end up with the equation $\displaystyle{0}=-{4}\usepackage{cmbright}\Huge\$ . Since this is false, you cannot find numbers that make both equations true.