`***`Lời giải+Giải thích`***`
`(x+1)^3-(x+3)(x^2-3x+9)=(x-3)^3+2(2x+1)^2-(x^3-5x+1)`
`<=>x^3+3x^2+3x+1-x^3-27=x^3-9x^2+27x-27+2(4x^2+4x+1)-x^3+5x-1`
`<=>(x^3-x^3-x^3+x^3)+(3x^2+9x^2-8x^2)+(3x-27x-8x-5x)+(1-27+27-2+1)=0`
`<=>0+4x^2-37x+2=0`
`<=>x(4x-37)=0`
`<=>x=0` hoặc `x=37/4`
Vậy `S={0;37/4}`