\[\left( 1 + a^{- 3} \right)(a + 1)^{- 2} =\]
\[= \left( 1 + \frac{1}{a^{3}} \right)\left( \frac{1}{a + 1} \right)^{2} =\]
\[= \frac{a^{3} + 1}{a^{3}} \cdot \frac{1}{(a + 1)^{2}} =\]
\[= \frac{a² - a + 1}{a^{3}(a + 1)}\]