`(x-5x)(x+2)+4(x-2)(x+1)+2(x-2)(x+2)=0`
`⇔ -4x^2 - 8x + 4x^2 - 4x - 8 + 2x^2 -8 = 0`
`⇔ (-4x^2+4x^2+2x^2) - (8x+4x) - (8+8) = 0`
`⇔ 2x^2 - 12x - 16 = 0`
`⇔ 2x^2 - 12x = 16`
`⇔ x^2 - 6x = 8`
`⇔ x^2 - 6x + (-3)^2 = 8 + (-3)^2`
`⇔ x^2 - 6x + 9 = 17`
`⇔ x^2 - 2x*3 + 3^2 = 17`
`⇔ (x-3)^2 = 17`
`⇔ |x-3| = sqrt{17}`
`1)` `x - 3 = sqrt{17} ⇔ x = sqrt{17} + 3`
`2)` `x - 3 = sqrt{17} ⇔ x = 3 - sqrt{17}`
Vậy `S = {sqrt{17}+3,3-sqrt{17}}`
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`(8x-3)(3x+2)+(4x+7)(x+4)=(2x+1)(5x-1)-33`
`⇔ 24x^2 + 7x - 6 + 4x^2 + 23x + 28 = 10x^2+3x-1-33`
`⇔ 28x^2 + 30x + 22 = 10x^2 + 3x - 34`
`⇔ 28x^2 + 30x + 22 - 10x^2 - 3x + 34 = 0`
`⇔ 18x^2 + 27x + 56 = 0`
`⇔ 18x^2 + 27x = -56`
`⇔ x^2 + 3/2x = -28/9`
`⇔ x^2 + 3/2x + (3/4)^2 = -28/9 + (3/4)^2`
`⇔ x^2 + 3/2x + 9/16 = -367/144`
`⇔ x^2 + 2x*3/4 + (3/4)^2 = -367/144`
`⇔ (x+3/4)^2 = -367/144`
`⇔ |x+3/4| = sqrt{(-367)/144}` (vô lý)
`⇒ x ∈ ∅`
Vậy `S = ∅`
