PT \(\Leftrightarrow x^2-2x+1+y^2-4y+4=0\)
\(\Leftrightarrow\left(x-1\right)^2+\left(y-2\right)^2=0\)
Thấy : \(\left\{{}\begin{matrix}\left(x-1\right)^2\ge0\\\left(y-2\right)^2\ge0\end{matrix}\right.\)
\(\Rightarrow\left(x-1\right)^2+\left(y-2\right)^2\ge0\)
- Dấu " = " xảy ra \(\Leftrightarrow\left\{{}\begin{matrix}x-1=0\\y-2=0\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=1\\y=2\end{matrix}\right.\)
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