\(A=\left(x+2\right)^2+\left(y-\dfrac{1}{5}\right)^2-10\ge-10\)
Dấu "=" xảy ra khi:
\(\left\{{}\begin{matrix}\left(x+2\right)^2=0\\\left(y-\dfrac{1}{5}\right)^2=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-2\\y=\dfrac{1}{5}\end{matrix}\right.\)