Correct. Factor out 3 and set the equation to zero: $\displaystyle{{x}}^{{2}}-{10}{x}+{15}={0}\usepackage{cmbright}\Huge\$ ; now use completing the square to find the roots. Rewrite the equation as $\displaystyle{{x}}^{{2}}-{10}{x}=-{15}\usepackage{cmbright}\Huge\$ and add 25 to both sides to create a perfect square: $\displaystyle{{x}}^{{2}}-{10}{x}+{25}=-{15}+{25}\usepackage{cmbright}\Huge\$ . This creates $\displaystyle{{\left({x}-{5}\right)}}^{{2}}={10}\usepackage{cmbright}\Huge\$ , so the roots are $\displaystyle{x}={5}+\sqrt{{{10}}}\usepackage{cmbright}\Huge\$ and $\displaystyle{x}={5}-\sqrt{{{10}}}\usepackage{cmbright}\Huge\$ .