Answer:
[tex]\large\boxed{4\sqrt3}[/tex]
Step-by-step explanation:
[tex]\text{A geometric mean of}\ a\ \text{and}\ b:\\\\\sqrt{ab}\\\\\text{We have}\ a=4,\ b=12.\\\\\text{Substitute:}\\\\\sqrt{4\cdot12}=\sqrt{48}=\sqrt{16\cdot3}\qquad\text{use}\ \sqrt{ab}=\sqrt{a}\cdot\sqrt{b}\\\\=\sqrt{16}\cdot\sqrt3=4\sqrt3[/tex]
