\(\left(x+2\right)^2=81\)
\(\Rightarrow\left[{}\begin{matrix}\left(x+2\right)^2=9^2\\\left(x+2\right)^2=\left(-9\right)^2\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x+2=9\\x+2=-9\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=9-2\\x=-9-2\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=7\\x=-11\end{matrix}\right.\)
Vậy x=7; x=-11
