(2x+5)2=(x+2)2
<=> (2x+5)2-(x+2)2=0
<=> (2x+5-x-2)(2x+5+x+2)=0
<=> (x+3)(4x+7)=0
<=>\(\left[{}\begin{matrix}x+3=0\\4x+7=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-3\\x=\dfrac{-7}{4}\end{matrix}\right.\)
Vậy S= \(\left\{-3;\dfrac{-7}{4}\right\}\)