`c) (2x - 1)(x^2 - x + 1) = 2x^3 - 3x^2 + 2`
`<=>2x(x^2 - x + 1)-1(x^2 - x + 1)=2x^3 - 3x^2 + 2`
`<=>2x^3-2x^2+2x-x^2+x-1=2x^3 - 3x^2 + 2`
`<=>2x^2-2x^3-2x^2-x^2+3x^2+x+2x=1+2`
`<=>3x=3`
`<=>x=1`
Vậy `S={1}`
`d) (x + 1)(x + 2)(x + 5) - x^3 - 8x^2 + 7 = 0`
`<=>[x(x+2)+1(x+2)](x + 5) - x^3 - 8x^2 + 7 = 0`
`<=>(x^2+2x+x+2)(x + 5) - x^3 - 8x^2 + 7 = 0`
`<=>(x^2+3x+2)(x+5) -x^3 - 8x^2 + 7 = 0`
`<=>x^2(x+5)+3x(x+5)+2(x+5)-x^3 - 8x^2 + 7 = 0`
`<=>x^3+5x^2+3x^2+15x+2x+10-x^3 - 8x^2 + 7 = 0`
`<=>x^3+8x^2+17x+10-x^3 - 8x^2 + 7 = 0`
`<=>17x=-10-7`
`<=>17x=-17`
`<=>x=-1`
Vậy `S={-1}`