`(2x - 7)^2 + 6(7 - 2x)(x - 3) = 0`
`<=> (7 - 2x)^2 + 6(7 - 2x)(x - 3) = 0`
`<=> (7 - 2x). [(7 - 2x) + 6(x - 3)] = 0`
`<=> (7 - 2x). (7 - 2x + 6x - 18) = 0`
`<=> (7 - 2x). (4x - 11) = 0`
`<=>` \(\left[ \begin{array}{l}7-2x=0\\4x-11=0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}2x=7\\4x=11\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=\frac{7}{2}\\x=\frac{11}{4}\end{array} \right.\)
Vậy `S = {7/2; 11/4}`
