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 with the sign of the radicand. The expression $\displaystyle{{b}}^{{2}}-{4}{a}{c}\usepackage{cmbright}\Huge\$ should simplify to $\displaystyle-{16}\usepackage{cmbright}\Huge\$ , not 16.