\[= \frac{a^{3} + a}{\left( a^{2} + 1 \right)\left( a^{2} - 1 \right)} =\]
\[= \frac{a \bullet \left( a^{2} + 1 \right)}{\left( a^{2} + 1 \right)\left( a^{2} - 1 \right)} = \frac{a}{a^{2} - 1}.\]
\[= \frac{0}{(a + 1)(a + 2)(a + 3)} = 0.\]
\[a^{2} + 5a + 6 = 0\]
\[D = 25 - 24 = 1\]
\[a_{1} = \frac{- 5 - 1}{2} = - 3;\ \]
\[a_{2} = \frac{- 5 + 1}{2} = - 2.\]
\[a^{2} + 4a + 3 = 0\]
\[D = 16 - 12 = 4\]
\[a_{1} = \frac{- 4 - 2}{2} = - 3;\]
\[a_{2} = \frac{- 4 + 2}{2} = - 1.\]
\[(a + 1)^{2} + a + 1 = 0\]
\[a^{2} + 3a + 2 = 0\]
\[D = 9 - 8 = 1\]
\[a_{1} = \frac{- 3 - 1}{2} = - 2;\]
\[a_{2} = \frac{- 3 + 1}{2} = - 1.\]
\[Ответ:\ \ 0.\]