You may have miscalculated the discriminant $\displaystyle{{b}}^{{2}}-{4}{a}{c}\usepackage{cmbright}\Huge\$ , thinking that $\displaystyle{c}=-{2}\usepackage{cmbright}\Huge\$ , but you need to rewrite the equation as $\displaystyle{2}{{x}}^{{2}}-{4}{x}+{2}={0}\usepackage{cmbright}\Huge\$ . In this equation, $\displaystyle{a}={2},{b}=-{4}\usepackage{cmbright}\Huge\$ , and $\displaystyle{c}={2}\usepackage{cmbright}\Huge\$ .