Đặt \(x+3=t\)
\(\Rightarrow\left(t-1\right)^4+\left(t+1\right)^4-16=0\)
\(\Leftrightarrow2t^4+12t^2+2-16=0\)
\(\Leftrightarrow t^4+6t^4-7=0\Rightarrow\left[{}\begin{matrix}t^2=1\\t^2=-7\left(l\right)\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}t=1\\t=-1\end{matrix}\right.\) \(\Rightarrow\left[{}\begin{matrix}x=-2\\x=-4\end{matrix}\right.\)