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