You may have recognized that $\displaystyle{{7}}^{{2}}={49}\usepackage{cmbright}\Huge\$ , but $\displaystyle{{\left({6}{x}+{7}\right)}}^{{2}}={36}{{x}}^{{2}}+{84}{x}+{49}\usepackage{cmbright}\Huge\$ , which is not equal to the given trinomial. 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\$ . Remember that $\displaystyle{9}{{x}}^{{2}}={{\left({3}{x}\right)}}^{{2}}\usepackage{cmbright}\Huge\$ and $\displaystyle{49}={{7}}^{{2}}\usepackage{cmbright}\Huge\$ .