Question

what is a geometric mean?

Answer 1

Suppose two numbers a and b are in geometric mean then we represent it as like this-

$g.m. = {(a \times b)}^{ \frac{1}{2} }$

Answer 2

If suppose we consider that ABC is a triangle and point P lies between the line A and B then by doing construction draw a line joining points B and P then your geometric mean will be as follows:
BP×BP =AB×BC