`3x^{2}-7-4x=0`
`<=> 3x^{2}-4x-7=0`
`<=>3x^{2}+3x-7x-7=0`
`<=>(3x^{2}+3x)-(7x+7)=0`
`<=>3x(x+1)-7(x+1)=0`
`<=> (x+1)(3x-7)=0`
`<=>`$\left[\begin{matrix} x+1=0\\ 3x-7=0\end{matrix}\right.$
`<=>` \(\left[{}\begin{matrix}x=-1\\x=\dfrac{7}{3}\end{matrix}\right.\)
vậy `S={-1;(7)/(3)}`