vd:\(\left|3x-9\right|=\left|x+1\right|\)
\(\Leftrightarrow\left[{}\begin{matrix}3x-9=x+1\\3x-9=-x-1\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}3x-x=9+1\\3x+x=9-1\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}2x=10\\4x=8\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=5\\x=2\end{matrix}\right.\)
S=\(\left\{5;2\right\}\)