Multiply the polynomial by $\displaystyle-{1}\usepackage{cmbright}\Huge\$ : $\displaystyle{\left(-{1}\right)}{\left(-{24}{{d}}^{{2}}+{16}{d}-{12}\right)}\usepackage{cmbright}\Huge\$

Distribute $\displaystyle-{1}\usepackage{cmbright}\Huge\$ to each term: $\displaystyle{\left(-{1}\right)}{\left(-{24}{{d}}^{{2}}\right)}+{\left(-{1}\right)}{\left({16}{d}\right)}+{\left(-{1}\right)}{\left(-{12}\right)}\usepackage{cmbright}\Huge\$

Multiply each coefficient by $\displaystyle-{1}\usepackage{cmbright}\Huge\$ : $\displaystyle{24}{{d}}^{{2}}+{\left(-{16}{d}\right)}+{12}\usepackage{cmbright}\Huge\$

Rewrite addition of a negative term as subtraction: $\displaystyle{24}{{d}}^{{2}}-{16}{d}+{12}\usepackage{cmbright}\Huge\$