\(x^4-104+13x^3-8x=0\Leftrightarrow\left(x^4+13x^3\right)+\left(-8x-104\right)=0\)
\(\Leftrightarrow x^3\left(x+13\right)-8\left(x+13\right)=0\Leftrightarrow\left(x^3-8\right)\left(x+13\right)=0\)
\(\Leftrightarrow\left\{{}\begin{matrix}x^3-8=0\\x+13=0\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x^3=8\\x=-13\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x=2\\x=-13\end{matrix}\right.\) vậy \(x=2;x=-13\)
