\(\Leftrightarrow x\left(x+1\right)\left(x-1\right)\left(x+2\right)-3=0\)
\(\Leftrightarrow\left(x^2+x\right)\left(x^2+x-2\right)-3=0\)
Đặt \(x^2+x=t\)
\(\Rightarrow t^2\left(t-2\right)-3=0\Leftrightarrow t^2-2t-3=0\Rightarrow\left[{}\begin{matrix}t=-1\\t=3\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x^2+x=-1\\x^2+x=3\end{matrix}\right.\) \(\Rightarrow\left[{}\begin{matrix}x^2+x+1=0\left(vn\right)\\x^2+x-3=0\left(casio\right)\end{matrix}\right.\)