You may have confused this expression with a perfect square trinomial, which has the same factor twice. However, a binomial in the form $\displaystyle{{a}}^{{3}}+{{b}}^{{3}}\usepackage{cmbright}\Huge\$ is factored as $\displaystyle{\left({a}+{b}\right)}{\left({{a}}^{{2}}-{a}{b}+{{b}}^{{2}}\right)}\usepackage{cmbright}\Huge\$ .