a) (x - 3)^3 - (x - 3) (x^2 + 3x + 9) + 9(x + 1)^2 =15
(=) (x^3-9x^2+27x-27)-(x^3-27)+9(x^2+2x+1)=15
(=) x^3-9x^2+27x-27-x^3+27+9x^2+18x+9=15
(=) 45x+9=15
(=) 45x=6
(=) x=6/45=2/15
Vậy x=2/15
b) x(x - 5) (x + 5) - (x - 2) (x^2 + 2x +4) = -17
(=) x(x^2-25)-(x^3-8)=-17
(=) x^3-25x-x^3+8=-17
(=) -25x+8=-17
(=) -25x=-25
(=) x=1
Vậy x=1