\(\Rightarrow\left[{}\begin{matrix}2x+1=\dfrac{4}{5}\\2x+1=-\dfrac{4}{5}\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}2x=-\dfrac{1}{5}\\2x=-\dfrac{9}{5}\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=-\dfrac{1}{10}\\x=-\dfrac{9}{10}\end{matrix}\right.\)
\(\left(2x+1\right)^2=\dfrac{16}{25}\)
<=> \(\left(2x+1\right)^2-\left(\dfrac{4}{5}\right)^2=0\)
<=> \(\left(2x+1+\dfrac{4}{5}\right)\left(2x+1-\dfrac{4}{5}\right)=0\)
<=> \(\left(2x+\dfrac{9}{5}\right)\left(2x+\dfrac{1}{5}\right)=0\)
<=> \(\left[{}\begin{matrix}2x+\dfrac{9}{5}=0\\2x+\dfrac{1}{5}=0\end{matrix}\right.\)
<=> \(\left[{}\begin{matrix}x=-\dfrac{9}{10}\\x=-\dfrac{1}{10}\end{matrix}\right.\)
