This is a graph of the equation $\displaystyle{y}={{x}}^{{2}}+{x}.\usepackage{cmbright}\Huge\$ The parabola crosses through $\displaystyle{\left({0},{0}\right)}\usepackage{cmbright}\Huge\$ on this graph, but if you substitute $\displaystyle{\left({0},{0}\right)}\usepackage{cmbright}\Huge\$ in for $\displaystyle{\left({x},{y}\right)}\usepackage{cmbright}\Huge\$ in the original equation, you do not get a true statement.