1. Objectives
Use geometric mean to find segment lengths in right triangles.
Apply similarity relationships in right triangles to solve problems.

2. Vocabulary
geometric mean

3. The geometric mean of two positive numbers is the positive square root of their product.
Consider the proportion In this case, the means of the proportion are the same number, and that number (x) is the geometric mean of the extremes.

4. Example 1A: Finding Geometric Means
Find the geometric mean of each pair of numbers. If necessary, give the answer in simplest radical form.
4 and 9
Let x be the geometric mean.
Def. of geometric mean
Cross multiply
x = 6
Find the positive square root.

5. Example 1b: Finding Geometric Means
Find the geometric mean of each pair of numbers. If necessary, give the answer in simplest radical form.
6 and 15
Let x be the geometric mean.
Def. of geometric mean
Cross multiply
Find the positive square root.

6. Example 1c: Finding Geometric Means
Find the geometric mean of each pair of numbers. If necessary, give the answer in simplest radical form.
2 and 8
Let x be the geometric mean.
Def. of geometric mean
Cross multiply
Find the positive square root.

7. In a right triangle, an altitude drawn from the vertex of the right angle to the hypotenuse forms two right triangles.

8. Example: Identifying Similar Right Triangles
Write a similarity statement comparing the three triangles.
Sketch the three right triangles with the angles of the triangles in corresponding positions. Z W
By Theorem 8-1-1, ∆UVW ~ ∆UWZ ~ ∆WVZ.

9. Similarity in Right Triangles
8-1
Similarity in Right Triangles
You can use Theorem to write proportions comparing the side lengths of the triangles formed by the altitude to the hypotenuse of a right triangle.
All the relationships in red involve geometric means.
Holt Geometry

10. Example 1 m = 2, n = 10, h = ___ 2 2 10 10 c a b n m h c a b n m h a m

11. Example 2 m = 2, n = 10, b = ___ 2 2 10 10 12 c a b n m h c a b n m h

12. Example 2 n = 27, c = 30, b = ___ 27 27 30 c a b n m h a m h c a b n m

13. Once you’ve found the unknown side lengths, you can use the Pythagorean Theorem to check your answers.
Helpful Hint