1. The geometric mean is the positive number x such that: A X X B

2. To find the geometric mean: Example: Find the geometric mean between 4 and 16. Write a proportion with X in the two mean positions: 4 X X 16 Cross multiply: X 2 = 64 Find the square root, simplify. X = 8

3. Another example: Find the geometric mean between 4 and 20. 4 X X 20 X 2 = 80 X = 80 X = 4 5

4. What if you know the geometric mean? Example: 6 is the geometric mean between 9 and what other number: Set up the proportion this way: X 6 6 9 Cross multiply: 9X = 36 And finish! X = 4 *no square root!!!