\[(a + 2)^{3} = a³ + 8\]
\[(a + 2)(a + 2)(a + 2) = a + 8\]
\[\left( a^{2} + 4a + 4 \right)(a + 2) = a + 8\]
\[a^{3} + 2a^{2} + 4a^{2} + 8a + 4a + 8 =\]
\[= a^{3} + 8\]
\[a^{3} + 6a^{2} + 12a + 8 \neq a^{3} + 8\]
\[ч.т.д.\]