Question

Answer 1

=>x^2+2x+9=9

=>x^2+2x=0

=>x(x+2)=0

=>x=0 hoặc x=-2

Answer 2

\(\sqrt{x^2+2x+9}=3\\ \Leftrightarrow\sqrt{\left(x^2+2x+9\right)^2}=3^2\\ \Leftrightarrow x^2+2x+9-9=0\\ \Leftrightarrow x^2+2x=0\\ \Leftrightarrow x\left(x+2\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=0\\x+2=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=0\\x=-2\end{matrix}\right.\)