$\text{Đáp án + Giải thích các bước giải:}$
`2(9x^{2}+6x+1)=(3x+1)(x-2)`
`<=>2(3x+1)^{2}=(3x+1)(x-2)`
`<=>2(3x+1)^{2}-(3x+1)(x-2)=0`
`<=>(3x+1)[2(3x+1)-(x-2)]=0`
`<=>(3x+1)(6x+2-x+2)=0`
`<=>(3x+1)(5x+4)=0`
`<=>` \(\left[ \begin{array}{l}3x+1=0\\5x+4=0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}3x=-1\\5x=-4\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=-\dfrac{1}{3}\\x=-\dfrac{4}{5}\end{array} \right.\)
`\text{Vậy}` `S={-(1)/(3);-(4)/(5)}`
