Đáp án:
` a, 2(5x - 8) - 3(4x - 5) = 4(3x - 4) +11`
`<=> 10x - 16 - 12x + 15 = 12x - 16 + 11`
`<=> 10x - 12x - 12x = -16 + 11 + 16 - 15`
`<=> -14x = -4`
`<=> x = 2/7`
Vậy `S={ 2/7}`
`b, 2x(6x - 2x^2) + 3x^2(x - 4) = 8`
`<=> 12x^2 - 4x^3 + 3x^3 - 12x^2 = 8`
`<=> -x^3 = 8`
`<=> x^3 = -8`
`<=> x= -2`
Vậy `S={ -2}`