\(\Leftrightarrow\left\{{}\begin{matrix}x+3=0\\x-1=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-3\\x=1\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x+3=0\\x-1=0\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=-3\\x=1\end{matrix}\right.\)
\(\Rightarrow x\in\left\{-3,1\right\}\)
\(x\in\left\{-3;1\right\}\)