You probably correctly substituted $\displaystyle{a}={1},{b}={0}\usepackage{cmbright}\Huge\$ , and $\displaystyle{c}={4}\usepackage{cmbright}\Huge\$ into the Quadratic Formula, $\displaystyle{x}=\frac{{-{b}\pm\sqrt{{{{b}}^{{2}}-{4}{a}{c}}}}}{{{2}{a}}}\usepackage{cmbright}\Huge\$ , but made a mistake simplifying the expression. You cannot simplify $\displaystyle\frac{\sqrt{{16}}}{{2}}\usepackage{cmbright}\Huge\$ to get $\displaystyle\sqrt{{8}}\usepackage{cmbright}\Huge\$ .