Cách thứ nhất :
`3x(x-2020) - x+2020 =0`
`=> 3x(x-2020) -(x-2020) =0`
`=> (3x-1)(x-2020) =0`
`=> (3x-1)(x-2020) =0`
`=>` \(\left[ \begin{array}{l}3x-1 =0 \\x-2020 =0\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=\dfrac{1}{3}\\x=2020\end{array} \right.\)
Vậy `S \in {1/3 ; 2020}`
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Cách thứ hai :
`3x(x-2020) - x +2020 =0`
`=> 3x^2 - 6060x - x +2020 =0`
`=> 3x^2 - 6061x +2020 =0`
`=>(3x-1)(x-2020) =0`
`=>` \(\left[ \begin{array}{l}3x-1 =0 \\x-2020 =0\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=\dfrac{1}{3}\\x=2020\end{array} \right.\)
Vậy `S \in {1/3 ; 2020}`