\(\left(2x+1\right)^2-4\left(x+2\right)^2=9\)
\(\Leftrightarrow\left(4x^2+4x+1\right)-4\left(x^2+4x+4\right)=9\)
\(\Leftrightarrow4x^2+4x+1-4x^2-16x-16=9\)
\(\Leftrightarrow4x+1-16x-25=0\)
\(\Leftrightarrow-12x-24=0\)
\(\Leftrightarrow-12\left(x+2\right)=0\)
\(\Leftrightarrow x=-2\)
Vậy x = -2