\[a^{3} + b^{3} = (a + b)\left( a^{2} + ab + b^{2} \right)\]
\[(a + b)\left( a^{2} - ab + b^{2} \right) \neq\]
\[\neq (a + b)(a^{2} + ab + b^{2})\]
\[Не\ тождественно.\]