\[x^{6} - 7x^{3} - 8 = 0\]
\[Пусть\ x^{3} = y:\]
\[y^{2} - 7y - 8 = 0\]
\[y_{1} + y_{2} = 7;\ \ \ y_{1} \cdot y_{2} = - 8\]
\[y_{1} = 8;\ \ \ y_{2} = - 1.\]
\[1)\ x^{3} = 8\]
\[x = 2.\]
\[2)\ x^{3} = - 1\]
\[x = - 1.\]
\[Ответ:x = - 1;x = 2.\]