`a) (2x-1)(3x-2)-6x(x+1)=8`
`<=> 6x^2-4x-3x+2-6x^2-6x=8`
`<=> -13x=6`
`<=> x=-6/13`
Vậy `S={-6/13}`
`b) 3x(2x-5)-6x^2=-13x+12`
`<=> 6x^2-15x-6x^2+13x=12`
`<=> -2x=12`
`<=> x=-6`
Vậy `S={-6}`
`c) (x-1)(4x-3)-4x(x-5)=5`
`<=>4x^2-3x-4x+3-4x^2+20x=5`
`<=> 13x=2`
`<=>x=2/13`
Vậy `S={2/13}`