+ Theo BĐT AM - GM :
\(\left(x+2\right)^2+\frac{2}{x+2}=\left(x+2\right)^2+\frac{1}{x+2}+\frac{1}{x+2}\)
\(\ge3\sqrt[3]{\left(x+2\right)^2\cdot\frac{1}{x+2}\cdot\frac{1}{x+2}}=3\)
Dấu "=" \(\Leftrightarrow\left(x+2\right)^2=\frac{1}{x+2}\Leftrightarrow x=-1\)