a/ `(x-1)(x^2+x+1)-x(x^2+2)=3`
`<=>x^3-1-x^3-2x=3`
`<=>-2x-1=3`
`<=>-2x=3+1`
`<=>-2x=4`
`<=>x=4:(-2)`
`<=>x=-2`
Vậy `x=-2`.
b/ `(x+2)(x^2-2x+4)+x(x+2)(2-x)=0`
`<=>(x^3+8)+x(4-x^2)=0`
`<=>x^3+8+4x-x^3=0`
`<=>4x+8=0`
`<=>4x=0-8`
`<=>4x=-8`
`<=>x=-2`
Vậy `x=-2`.
c/ `(x-2)(x^2+2x+4)-(x-1)(x^2+x+1)=7x`
`<=>(x^3-8)-(x^3-1)=7x`
`<=>x^3-8-x^3+1=7x`
`<=>-7=7x`
`<=>x=-7:7`
`<=>x=-1`
Vậy `x=-1`.
d/ `(x-3)(x^2-5x+1)-(x^2+1)(x-8)=0`
`<=>(x^3-5x^2+x-3x^2+15x-3)-(x^3-8x^2+x-8)=0`
`<=>x^3-5x^2+x-3x^2+15x-3-x^3+8x^2-x+8)=0`
`<=>15x+5=0`
`<=>5(x+1)=0`
`<=>x+1=0`
`<=>x=0-1`
`<=>x=-1`
Vậy `x=-1`.
