\(\Leftrightarrow\left(x^2+4x+2\right)^2-\left(x^2\right)^2\le0\)
\(\Leftrightarrow\left(x^2+4x+2-x^2\right)\left(x^2+4x+2+x^2\right)\le0\)
\(\Leftrightarrow\left(2x+1\right)\left(x^2+2x+1\right)\le0\)
\(\Leftrightarrow\left(2x+1\right)\left(x+1\right)^2\le0\)
\(\Rightarrow\left[{}\begin{matrix}x=-1\\x\le-\frac{1}{2}\end{matrix}\right.\) \(\Rightarrow x\le-\frac{1}{2}\)