\(\sqrt{x^2-6x+9}=3\)
\(\Leftrightarrow\sqrt{\left(x-3\right)^2}=3\)
\(\Leftrightarrow\left|x-3\right|=3\)
\(\Leftrightarrow\left[{}\begin{matrix}x-3=3\\x-3=-3\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=6\\x=0\end{matrix}\right.\)
ĐKXĐ:\(x^2-6x+9\ge0\Rightarrow\left(x-3\right)^2\ge0\left(luôn.đúng\right)\)
\(\sqrt{x^2-6x+9}=3\\ \Leftrightarrow\sqrt{\left(x-3\right)^2}=3\\ \Leftrightarrow\left|x-3\right|=3\\ \Leftrightarrow\left[{}\begin{matrix}x-3=3\\x-3=-3\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=6\\x=0\end{matrix}\right.\)
