Multiply the polynomial by $\displaystyle-{1}\usepackage{cmbright}\Huge\$ : $\displaystyle{\left(-{1}\right)}{\left({2}{{p}}^{{3}}-{9}{p}-{4}\right)}\usepackage{cmbright}\Huge\$

Distribute $\displaystyle-{1}\usepackage{cmbright}\Huge\$ to each term in the polynomial: $\displaystyle{\left(-{1}\right)}{\left({2}{{p}}^{{3}}\right)}+{\left(-{1}\right)}{\left(-{9}{p}\right)}+{\left(-{1}\right)}{\left(-{4}\right)}\usepackage{cmbright}\Huge\$

Multiply each coefficient by $\displaystyle-{1}\usepackage{cmbright}\Huge\$ : $\displaystyle{\left(-{2}{{p}}^{{3}}\right)}+{9}{p}+{4}\usepackage{cmbright}\Huge\$ = $\displaystyle-{2}{{p}}^{{3}}+{9}{p}+{4}\usepackage{cmbright}\Huge\$