\(\sqrt{x^2+5x+4}\ge2x+2\) (ĐKXĐ: \(x\ge-1\))
\(\Leftrightarrow x^2+5x+4=4x^2+8x+4\)
\(\Leftrightarrow-3x^2-3x=0\)
\(\Leftrightarrow-3x\left(x+1\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}-3x=0\\x+1=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x=-1\end{matrix}\right.\) (TMĐK)
Vậy \(S=\left\{0;-1\right\}\)