\(x^2+3x+1< 0\)
\(\Rightarrow x^2+3x+\dfrac{9}{4}-\dfrac{5}{4}< 0\)
\(\Rightarrow\left(x+\dfrac{3}{2}\right)^2< \dfrac{5}{4}\)
\(\Rightarrow\left[{}\begin{matrix}x+\dfrac{3}{2}< \sqrt{\dfrac{5}{4}}\\x+\dfrac{3}{2}< -\sqrt{\dfrac{5}{4}}\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x< \dfrac{-3+\sqrt{5}}{2}\\x< \dfrac{-3-\sqrt{5}}{2}\end{matrix}\right.\)