Câu 14:
\(\sqrt{x^2-6x+9}=3\)
\(\Leftrightarrow\sqrt{\left(x-3\right)^2}=3\)
\(\Leftrightarrow\left|x-3\right|=3\)
\(\Leftrightarrow\left[{}\begin{matrix}x-3=3\left(x\ge3\right)\\x-3=-3\left(x< 3\right)\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=6\left(tm\right)\\x=0\left(tm\right)\end{matrix}\right.\)
⇒ Chọn D
Câu 15.
\(x-3=\left(\sqrt{x}\right)^2-\left(\sqrt{3}\right)^2=\left(\sqrt{x}-\sqrt{3}\right)\left(\sqrt{x}+\sqrt{3}\right)\)
⇒ Chọn B
Câu 16:
\(x-5\sqrt{x}+6=\sqrt{x}-2\sqrt{x}-3\sqrt{x}+6\)
\(=\sqrt{x}\left(\sqrt{x}-2\right)-3\left(\sqrt{x}-2\right)=\left(\sqrt{x}-2\right)\left(\sqrt{x}-3\right)\)
⇒ Chọn D
