\(x^2-7x+6=0\)
\(\Leftrightarrow x^2-6x-x+6=0\)
\(\Leftrightarrow\left(x^2-6x\right)-\left(x-6\right)=0\)
\(\Leftrightarrow x\left(x-6\right)-\left(x-6\right)\)
\(\Leftrightarrow\left(x-1\right)\left(x-6\right)\)
\(\Leftrightarrow\left[{}\begin{matrix}x=1\\x=6\end{matrix}\right.\)
x\(^2\)-7x+6=0
\(\Leftrightarrow\)x\(^2\)-x-6x+6=0
\(\Leftrightarrow\)x(x-1)-6(x-1)=0
\(\Leftrightarrow\)(x-1)(x-6)=0
\(\Leftrightarrow\)\(\left[{}\begin{matrix}x-1=0\\x-6=0\end{matrix}\right.\)
\(\Leftrightarrow\)\(\left[{}\begin{matrix}x=1\\x=6\end{matrix}\right.\)
Vậy S={1;6}