Giải thích các bước giải:
`3x^3-18x=0`
`<=>3x(x^2-6)=0`
`<=>3x(x-sqrt6)(x+sqrt6)=0`
`=>`\(\left[ \begin{array}{l}3x=0\\x-\sqrt6=0\\x+\sqrt6=0\end{array} \right.\) `<=>`\(\left[ \begin{array}{l}x=0\\x=\sqrt6\\x=-\sqrt6\end{array} \right.\)
Vậy `S={0;+-\sqrt6}.`