Đáp án + Giải thích các bước giải:
`(x-2)^3-(x-3)(x^2+3x+9)+6(x+1)^2=15`
`<=>x^3-6x^2+12x-8-(x^3-27)+6(x^2+2x+1)=15`
`<=>x^3-6x^2+12x-8-x^3+27+6x^2+12x+6=15`
`<=>24x+25=15`
`<=>24x=-10`
`<=>12x=-5`
`<=>x=-5/12`
Vậy `S={-5/12}`
`(3x-5)(7-5x)-(5x+2)(2-3x)=4`
`<=>21x-15x^2-35+25x-(10x-15x^2+4-6x)=4`
`<=>21x-15x^2-35+25x-10x+15x^2-4+6x=4`
`<=>42x-39=4`
`<=>42x=43`
`<=>x=43/42`
Vậy `S={43/42}`
`(x+2)^2+(x-3)^2-2(x-1)(x+1)=9`
`<=>x^2+4x+4+x^2-6x+9-2(x^2-1)=9`
`<=>x^2+4x+4+x^2-6x+9-2x^2+2=9`
`<=>-2x+15=9`
`<=>-2x=-6`
`<=>x=3`
Vậy `S={3}`.