`sqrt{2x^2+7}+x=2`
Điều kiện:`x<=2`
`=>sqrt{2x^2+7}=2-x`
`=>2x^2+7=(2-x)^2`
`=2x^2+7=4-4x+x^2`
`=>2x^2-x^2+4x+7-4=0`
`=>x^2+4x+3=0`
`=>x^2+x+3x+3=0`
`=>x(x+1)+3(x+1)=0`
`=>(x+1)(x+3)=0`
`=>`\(\left[ \begin{array}{l}x+1=0\\x+3=0\end{array} \right.\)
`=>`\(\left[ \begin{array}{l}x=-1\text{(thỏa mãn)}\\x=-3\text{(thỏa mãn)}\end{array} \right.\)
Vậy `S={-1;-3}.`
