x^2+4x+4 +x^4+16x^3+96x^2+256x+256= -x^3-9x^2-28x-28
(x^2+4x+4)+ ( x^4 + 16x^3 + 96x^2 + 256x+ 256) + (x^3+9x^2+28x+28)=0
x^4+ 17 x^3 + 106x^2 + 288x + 288=0
x^4+ 3x^3+ 14x^3+42x^2+ 64x^2+192x+96x+288=0
(x+3)(x^3+14x^2+64x+96)=0
(x+3)(x^3+6x^2+8x^2+48x+16x+96)=0
(x+3)(x+6)(x^2+8x+16)=0
(x+3)(x+6)(x+4)^2=0
Vậy x=-3 hay x=-6 hay x=-4
cảm ơn bạn Anime lover :DD nhé