\(5x^3-5x=0\)
\(\Leftrightarrow5x\left(x^2-1\right)=0\)
\(\Leftrightarrow5x\left(x-1\right)\left(x+1\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}5x=0\\x-1=0\\x+1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=1\\x=-1\end{matrix}\right.\)
Vậy \(S=\left\{0;\pm1\right\}\)