Đáp án:
`2sqrt{3x^2+2x-1+1}=3x` `(x>=0; x>= -2/3)`
`<=> 2sqrt{3x^2+2x}=3x`
`<=> 4(3x^2+2x)=9x^2`
`<=> 12x^2+8x=9x^2`
`<=> 12x^2+8x-9x^2=0`
`<=> 3x^2+8x=0`
`<=> x(3x+8)=0`
`<=>`\(\left[ \begin{array}{l}x=0\\3x+8=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=0 \ (tm)\\x=-\dfrac{8}{3} \ (ktm)\end{array} \right.\)
`<=> x=0`
Vậy `S={0}`