\(\left(2x-7\right)\left(x+3\right)=x^2-9\\ \left(2x-7\right)\left(x+3\right)-x^2+9=0\\ \left(2x-7\right)\left(x+3\right)-\left(x^2-9\right)=0\\ \left(2x-7\right)\left(x+3\right)-\left(x-3\right)\left(x+3\right)=0\\ \left(x+3\right)\left(2x-7-x+3\right)=0\\ \left(x+3\right)\left(x-4\right)=0\\ \left[{}\begin{matrix}x+3=0< =>x=-3\\x-4=0< =>x=4\end{matrix}\right.\)
\(\left(2x-7\right)\left(x+3\right)=x^2-9\)
\(\Leftrightarrow\left(2x-7\right)\left(x+3\right)=\left(x-3\right)\left(x+3\right)\)
\(\Leftrightarrow\left(2x-7\right)\left(x+3\right)-\left(x-3\right)\left(x+3\right)=0\)
\(\Leftrightarrow\left(x+3\right)\left(2x-7-x+3\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+3=0\\x-4=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-3\\x=4\end{matrix}\right.\)
\(\left(2x-7\right)\left(x+3\right)=x^2-9\)
\(\Leftrightarrow\left(2x-7\right)\left(x+3\right)=\left(x-3\right)\left(x+3\right)\)
\(\Leftrightarrow\left(2x-7\right)\left(x+3\right)-\left(x-3\right)\left(x+3\right)=0\)
\(\Leftrightarrow\left(x+3\right)\left(2x-7-x+3\right)=0\)
\(\Leftrightarrow\left(x+3\right)\left(x-4\right)=0\)
\(x+3=0\) hoặc \(x-4=0\)
\(x\) \(=0-3\) \(x\) \(=0+4\)
\(x\) \(=-3\) \(x\) \(=4\)
\(\left(2x-7\right)\left(x+3\right)=x^2-9\)
\(\Leftrightarrow\left(2x-7\right)\left(x+3\right)=\left(x-3\right)\left(x+3\right)\)
\(\Leftrightarrow\left(2x-7\right)\left(x+3\right)-\left(x-3\right)\left(x+3\right)=0\)
\(\Leftrightarrow\left(x+3\right)\left[2x-7-\left(x-3\right)\right]=0\)
\(\Leftrightarrow\left(x+3\right)\left(2x-7-x+3\right)=0\)
\(\Leftrightarrow\left(x+3\right)\left(x-4\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+3=0\\x-4=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-3\\x=4\end{matrix}\right.\)
Vậy \(S=\left\{-3;4\right\}\).
