`(2x^2 - 10x )+ x - 5 = 0`
`⇔ 2x^2 - 10x + x - 5 = 0`
`⇔ 2x^2 - 9x - 5 = 0`
`⇔ 2x^2 + x - 10x - 5 = 0`
`⇔ ( 2x^2 + x ) + (-10x - 5 ) = 0`
`⇔ x(2x + 1) - 5(2x - 1) = 0`
`⇔ (x - 5)(2x + 1) = 0`
`⇔` \(\left[ \begin{array}{l}x-5=0\\2x +1=0\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}x=5\\x=-\frac{1}{2}\end{array} \right.\)
Vậy `S = { 5 ; -1/2}`