Respuesta :

[tex]\begin{gathered} \frac{9}{x}=\frac{x}{4} \\ We\text{ cross multiply, we have:} \\ x\cdot x=4\cdot9 \\ x^2=36 \\ \text{Take the square root of both sides, we have:} \\ \sqrt[]{x^2}=\sqrt[]{36} \\ x=6 \end{gathered}[/tex]