If you end up with $\displaystyle{0}={0}\usepackage{cmbright}\Huge\$ , then all the variables and constants have canceled each other out. This could only happen if the two equations were opposites. If you multiplied one of them by $\displaystyle-{1}\usepackage{cmbright}\Huge\$ , they would then be the same equation. Therefore they must have the same graph.