\(\left(2x+1\right)^2=\dfrac{1}{9}\)
⇒ \(\left[{}\begin{matrix}2x+1=\dfrac{1}{3}\\2x+1=-\dfrac{1}{3}\end{matrix}\right.\)
⇒ \(\left[{}\begin{matrix}x=-\dfrac{1}{3}\\x=-\dfrac{2}{3}\end{matrix}\right.\)
(2x+1)\(^2\)=(1/3)\(^2\)
TH1: 2x+1=1/3 TH2:2x+1=-1/3
2x =1/3-1 2x =-1/3-1
2x =-2/3 2x =-4/3
x =-2/3:2 x =-4/3:2
x =-1/3 x =-2/3
Vậy x∈{-1/3;-2/3}