Use the Quadratic Formula, $\displaystyle{x}=\frac{{-{b}\pm\sqrt{{{{b}}^{{2}}-{4}{a}{c}}}}}{{{2}{a}}}\usepackage{cmbright}\Huge\$ , with $\displaystyle{a}={1},{b}={5}\usepackage{cmbright}\Huge\$ , and $\displaystyle{c}={2}\usepackage{cmbright}\Huge\$ :

$\displaystyle{x}=\frac{{-{5}\pm\sqrt{{{{5}}^{{2}}-{4}{\left({1}\right)}{\left({2}\right)}}}}}{{{2}\cdot{1}}}=\frac{{-{5}\pm\sqrt{{{25}-{8}}}}}{{2}}=\frac{{-{5}\pm\sqrt{{17}}}}{{2}}=-\frac{{5}}{{2}}\pm\frac{\sqrt{{17}}}{{2}}\usepackage{cmbright}\Huge\$