`\text{~~Holi~~}`
`\sqrt{3x^2-2x+15}+\sqrt{3x^2-2x+8}=7`
`-> \sqrt{3x^2-2x+15}=7-\sqrt{3x^2-2x+8}`
`-> 3x^2-2x+15=49-14\sqrt{3x^2-2x+8}+3x^2-2x+8`
`-> 15=49-14\sqrt{3x^2-2x+8}+8`
`-> 15=57-14\sqrt{3x^2-2x+8}`
`-> 14\sqrt{3x^2-2x+8}=57-15`
`-> 14\sqrt{3x^2-2x+8}=42`
`-> \sqrt{3x^2-2x+8}=3`
`-> 3x^2-2x+8=9`
`-> 3x^2-2x+8-9=0`
`-> (3x+1)(x-1)=0`
`->` \(\left[ \begin{array}{l}3x+1=0\\x-1=0\end{array} \right.\)
`->` ``\(\left[ \begin{array}{l}x=\dfrac{-1}{3} \\x=1\end{array} \right.\)``
`\text{Vậy} S={-1/3,1}`
