You may have squared the left side and not the right side to get the incorrect equation $\displaystyle{x}-{4}=-{2}\usepackage{cmbright}\Huge\$ . That equation would have $\displaystyle{x}={2}\usepackage{cmbright}\Huge\$ as a solution. Make sure that you always perform the same operation on both sides of an equation. In this case you will get $\displaystyle{x}-{4}={4}\usepackage{cmbright}\Huge\$ . Solve this equation and check the solution back in the original equation.