\(\Leftrightarrow\left(x^2+1\right)^2+x\left(x^2+1\right)+2x\left(x^2+1\right)+2x^2=0\)
\(\Leftrightarrow\left(x^2+1\right)\left(x^2+1+x\right)+2x\left(x^2+1+x\right)=0\)
\(\Leftrightarrow\left(x^2+1+2x\right)\left(x^2+x+1\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x^2+2x+1=0\\x^2+x+1=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}\left(x+1\right)^2=0\\\left(x+\dfrac{1}{2}\right)^2+\dfrac{3}{4}=0\left(vn\right)\end{matrix}\right.\)
\(\Rightarrow x=-1\)