Tìm x: 3x^4 - 9x^3 = -9x^2 - 27x, x^2(x + 8) + x^2 = -8x, (x + 3) (x^2 - 3x + 5) = x^2 + 3x

tìm x:
b,3x^4-9x^3=-9x^2-27x
c,x^2(x+8)+x^2=-8x
d,(x+3)(x^2-3x+5)=x^2+3x