You may have chosen this equation because its solution is $\displaystyle{x}={5}\usepackage{cmbright}\Huge\$ . However, when you substitute $\displaystyle{x}=-{5}\usepackage{cmbright}\Huge\$ into the left side you get $\displaystyle\sqrt{{{2}{\left(-{5}\right)}-{1}}}=\sqrt{{-{11}}}\usepackage{cmbright}\Huge\$ , which is not a real number.