When a positive value is repeated in either the means or extremes position of a proportion, that value is referred to as a geometric mean (or mean proportional) between the other two values.
Example 1: Find the geometric mean between 4 and 25.
Let x = the geometric mean.
The geometric mean between 4 and 25 is 10.
Example 2: 12 is the geometric mean between 8 and what other value?
Let x = the other value.