\(x^2+4x+1=0\)
\(\Leftrightarrow x^2+4x+4-3=0\)
\(\Leftrightarrow\left(x+2\right)^2=3\)
\(\Leftrightarrow\left[{}\begin{matrix}x+2=\sqrt{3}\\x+2=-\sqrt{3}\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=\sqrt{3}-2\\x=-\sqrt{3}-2\end{matrix}\right.\)
Vậy \(x_1=\sqrt{3}-2;x_2=-\sqrt{3}-2\).