Although the product of the first terms is $\displaystyle{64}{{a}}^{{2}}\usepackage{cmbright}\Huge\$ , the product of the last terms is $\displaystyle-{9}\usepackage{cmbright}\Huge\$ , not 9, and the outer and inner products do not add up to $\displaystyle-{48}{a}\usepackage{cmbright}\Huge\$ . The first step is to determine if this a perfect square trinomial. Then you can use the fact that a trinomial in the form $\displaystyle{{r}}^{{2}}-{2}{r}{s}+{{s}}^{{2}}\usepackage{cmbright}\Huge\$ can be factored as $\displaystyle{{\left({r}-{s}\right)}}^{{2}}\usepackage{cmbright}\Huge\$ .