\(x^4+2x^3-3x^2-8x-4=0\Leftrightarrow x^3\left(x+2\right)-3x\left(x+2\right)-2\left(x+2\right)=0\Leftrightarrow\left(x+2\right)\left(x^3-3x-2\right)=0\)
\(\Leftrightarrow\left(x+2\right)\left(x^3-2x^2+2x^2-4x+x-2\right)=0\)(chỗ này bạn tự tách tiếp)
\(\Leftrightarrow\left(x-2\right)\left(x+2\right)\left(x+1\right)^2=0\Rightarrow\)hoặc x=2 hoặc x= -2 hoặc x=-1