Pt hoành độ giao điểm:
\(x^4+mx^2-1=m\)
\(\Leftrightarrow\left(x^2-1\right)\left(x^2+1\right)+m\left(x^2-1\right)=0\)
\(\Leftrightarrow\left(x^2-1\right)\left(x^2+m+1\right)=0\)
Pt có 4 nghiệm pb \(\Leftrightarrow\left\{{}\begin{matrix}m+1< 0\\m+1\ne-1\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}m< -1\\m\ne-2\end{matrix}\right.\) \(\Rightarrow m=\left\{-3;-4\right\}\)