\(\frac{4}{x}=\frac{x}{9}\)
\(\Rightarrow\)\(x\cdot x=4\cdot9\)
\(\Rightarrow x^2=36\)
\(x^2=6^2=\left(-6\right)^2\)
\(\Rightarrow\)\(\left[{}\begin{matrix}x=6\\x=-6\end{matrix}\right.\)
Vậy \(x\in\left\{6;-6\right\}\)
Ta có:
\(\frac{4}{x}=\frac{x}{9}\)
\(\Rightarrow x.x=4.9\)
\(\Leftrightarrow x^2=36=6^2=\left(-6\right)^2\)
Vậy: \(\left[{}\begin{matrix}x=6\\x=-6\end{matrix}\right.\)