\[x^{3} = 4x\]
\[x^{3} - 4x = 0\]
\[x\left( x^{2} - 4 \right) = 0\]
\[x(x + 2)(x - 2) = 0\]
\[x = 0;x = 2;x = - 2.\]
\[Ответ:x = 0;x = \pm 2.\]