You may have isolated the radical, but then squared the left side and not the right side, to get the incorrect equation $\displaystyle{5}{x}-{1}={5}{x}-{7}\usepackage{cmbright}\Huge\$ . That equation would not have a solution. Make sure that you always perform the same operation on both sides of an equation. In this case, you will get $\displaystyle{5}{x}-{1}={25}{{x}}^{{2}}-{70}{x}+{49}\usepackage{cmbright}\Huge\$ . Solve this quadratic equation and check the solutions back in the original equation.