`(3x^2+10x-8)=(5x^2-2x+10)^2`
`<=>(3x^2+10x-8+5x^2-2x+10)(3x^2+10x-8-5x^2+2x-10)=0`
`<=> (8x^2+8x+2)(-2x^2+12x-18)=0`
\(\Leftrightarrow\left[{}\begin{matrix}8x^2+8x+2=0\\-2x^2+12x-18=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{1}{2}\\x=3\end{matrix}\right.\)
Vậy `S={-1/2 ; 3}`.