Tìm `x` `5x (x - 2) - (2 - x) = 0`

 `5x(x-2)-(2-x)=0`

`⇔5x^2-10x-2+x=0`

`⇔5x^2-9x-2=0`

`⇔5x^2-10x+x-2=0`

`⇔5x(x-2)+(x-2)=0`

`⇔(x-2)(5x+1)=0`

`x-2=0` `⇔x=2`

`5x+1=0` `⇔x=frac{-1}{5}`

Vậy `S={2;frac{-1}{5}}`