Answer:
[tex]\large\boxed{3\sqrt7}[/tex]
Step-by-step explanation:
[tex]\text{Geometric mean:}\\\\\underbrace{\sqrt[n]{a_1\cdot a_2\cdot a_3\cdot...\cdot a_n}}_n\\\\\sqrt{7\cdot9}=\sqrt{9}\cdot\sqty7=3\sqrt7[/tex]
