c) \(\dfrac{x}{9}=\dfrac{4}{x}\Leftrightarrow x^2=36\\ \Leftrightarrow\left[{}\begin{matrix}x=6\\x=-6\end{matrix}\right.\)
d) ĐKXĐ: \(x\ge0\)
\(\left|\sqrt{x}-3\right|+3=9\\ \Leftrightarrow\left|\sqrt{x}-3\right|=6\\ \Leftrightarrow\left[{}\begin{matrix}\sqrt{x}-3=6\\\sqrt{x}-3=-6\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}\sqrt{x}=9\\\sqrt{x}=-3\left(vôlí\right)\end{matrix}\right.\Leftrightarrow x=81\)
c)\(\dfrac{x}{9}=\dfrac{4}{x}\Leftrightarrow x^2=9.4=36\)
\(\Rightarrow\sqrt{36}=x=6\)
d)\(\left|\sqrt{x}-3\right|+3=9\)
\(\Rightarrow\left[{}\begin{matrix}\sqrt{x}-3=6\\\sqrt{x}-3=-6\end{matrix}\right.\)\(\Rightarrow\left[{}\begin{matrix}\sqrt{x}=9\\\sqrt{x}=-3\left(vôlí\right)\end{matrix}\right.\)\(\Rightarrow x=81\)
