\(5x\left(x-9\right)-2x\left(9-x\right)=0\)
\(\Leftrightarrow5x\left(x-9\right)+20\left(x-9\right)=0\)
\(\Leftrightarrow5\left(x+4\right)\left(x-9\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x+4=0\\x-9=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=-4\\x=9\end{matrix}\right.\)
Vậy pt có tập nghiệm \(S=\left\{-4;9\right\}\)