\(x^3+2x^2+x-9x=0\)
\(x\left(x^2+2x+1-9\right)=0\)
\(x\left(x+1\right)^2-3^2=0\)
\(x\left(x+1-3\right)\left(x+1+3\right)=0\)
\(x\left(x-2\right)\left(x+4\right)=0\)
\(\Rightarrow x=0\) hoặc x - 2 = 0 hoặc x + 4 = 0
x = 0 ; x = 2 ; x = -4
Vậy x \(\in\)\(\left\{0;2;-4\right\}\)