You may have seen the perfect squares 25 and 36, disregarded the term $\displaystyle{8}{x}\usepackage{cmbright}\Huge\$ , and thought the equation could be rewritten as $\displaystyle{{\left({x}+{5}\right)}}^{{2}}={{6}}^{{2}}\usepackage{cmbright}\Huge\$ . You need to start with the middle term $\displaystyle{8}{x}\usepackage{cmbright}\Huge\$ , and use this to determine how to complete the square. In particular, you have to rewrite the equation so that the left side is $\displaystyle{{x}}^{{2}}+{8}{x}+{16}\usepackage{cmbright}\Huge\$ , then take square roots of both sides and solve for x.