a) \({x^3} - 8 = 0\)\( \Leftrightarrow \left( {x - 2} \right)\left( {{x^2} + 2x + 4} \right) = 0\) \( \Leftrightarrow \left[ \begin{array}{l}x - 2 = 0\\{x^2} + 2x + 4 = 0\end{array} \right.\) \( \Leftrightarrow \left[ \begin{array}{l}x = 2\\x = - 1 \pm i\sqrt 3 \end{array} \right.\)
b) \({x^3} + 8 = 0\)\( \Leftrightarrow \left( {x + 2} \right)\left( {{x^2} - 2x + 4} \right) = 0\)\( \Leftrightarrow \left[ \begin{array}{l}x + 2 = 0\\{x^2} - 2x + 4 = 0\end{array} \right.\) \( \Leftrightarrow \left[ \begin{array}{l}x = - 2\\x = 1 \pm i\sqrt 3 \end{array} \right.\)
