Giải pt :
\(\left(x+2\right)\left(3x+1\right)+x^2=4\)
\(\Leftrightarrow\left(x+2\right)\left(3x+1\right)+x^2-4=0\)
\(\Leftrightarrow\left(x+2\right)\left(3x+1\right)+\left(x^2-4\right)=0\)
\(\Leftrightarrow\left(x+2\right)\left(3x+1\right)+\left(x+2\right)\left(x-2\right)=0\)
\(\Leftrightarrow\left(x+2\right)\left[\left(3x+1\right)+\left(x-2\right)\right]=0\)
\(\Leftrightarrow\left(x+2\right)\left(3x+1+x-2\right)=0\)
\(\Leftrightarrow\left(x+2\right)\left(4x-1\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+2=0\\4x-1=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-2\\4x=1\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-2\\x=\dfrac{1}{4}\end{matrix}\right.\)
Tập nghiệm của pt là : \(S=\left\{-2;\dfrac{1}{4}\right\}\)