Remember that you should distribute the negative sign to both the $\displaystyle{2}{{x}}^{{2}}\usepackage{cmbright}\Huge\$ and the $\displaystyle{9}{x}\usepackage{cmbright}\Huge\$ because of the negative sign in $\displaystyle-{\left({2}{{x}}^{{2}}+{9}{x}\right)}\usepackage{cmbright}\Huge\$ .