$\displaystyle{{x}}^{{2}}+{16}{x}+{64}\usepackage{cmbright}\Huge\$ is the perfect square trinomial $\displaystyle{{\left({x}+{8}\right)}}^{{2}}\usepackage{cmbright}\Huge\$ . Recall that $\displaystyle{\left({a}-{r}\right)}{\left({a}+{r}\right)}\usepackage{cmbright}\Huge\$ is the difference of two squares, $\displaystyle{{a}}^{{2}}-{{r}}^{{2}}\usepackage{cmbright}\Huge\$ .