`2(x^2+8x+16)-x^2+4=0`
`<=>2x^2+16x+32-x^2+4=0`
`<=>x^2+16x+36=0`
`<=>(x+8)^2-28=0`
`<=>(x+8-\sqrt{28})(x+8+\sqrt{28}=0`
`<=>`\(\left[ \begin{array}{l}x+8+\sqrt{28}=0\\x+8-\sqrt{28}=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=-\sqrt{28}-8\\x=\sqrt{28}-8\end{array} \right.\)
Vậy `S={-\sqrt{28}-8;\sqrt{28}+8}`
