Question

Answer 1

\(ĐK:x\ge-2\\ PT\Leftrightarrow3\cdot\dfrac{1}{3}\sqrt{x+2}+2\sqrt{x+2}=9\\ \Leftrightarrow3\sqrt{x+2}=9\\ \Leftrightarrow\sqrt{x+2}=3\\ \Leftrightarrow x+2=9\\ \Leftrightarrow x=7\left(tm\right)\)

Answer 2

PT tương đương \(\sqrt{x+2}+2\sqrt{x+2}=9\)

Đặt \(\sqrt{x+2}=t\) (\(t\ge0\))

Khi đó PT trở thành \(t+2t=9\) \(\Leftrightarrow3t=9\) \(\Leftrightarrow\left\{{}\begin{matrix}t=3\\t=-3\left(l\right)\end{matrix}\right.\) 

\(\Leftrightarrow\sqrt{x+2}=3\) \(\Leftrightarrow x+2=9\) \(\Leftrightarrow x=7\)