1. The Pythagorean Theorem
5-7
The Pythagorean Theorem
Warm Up
Lesson Presentation
Lesson Quiz
Holt Geometry

2. Do Now
Classify each triangle by its angle measures. 1.
2. Simplify
3. If a = 6, b = 7, and c = 12, find a2 + b2 and find c2. Which value is greater?

3. Objectives
TSW use the Pythagorean Theorem and its converse to solve problems.
TSW use Pythagorean inequalities to classify triangles.

4. Vocabulary
Pythagorean triple

5. The Pythagorean Theorem is probably the most famous mathematical relationship. As you learned in Lesson 1-6, The Pythagorean Theorem states that in a right triangle, the sum of the squares of the lengths of the legs equals the square of the length of the hypotenuse.
a2 + b2 = c2

6. Example 1: Using the Pythagorean Theorem
Find the value of x.

7. Example 2: Using the Pythagorean Theorem
Find the value of x.

8. Example 3
Find the value of x.

9. Example 4
Find the value of x.

10. Example 5: Crafts Application
Randy is building a rectangular picture frame. He wants the ratio of the length to the width to be 3:1 and the diagonal to be 12 centimeters. How wide should the frame be? Round to the nearest tenth of a centimeter.

11. Example 5.9 Safety Application:
To prevent a ladder from shifting, safety experts recommend that the ratio of a : b be 4 : 1. How far from the base of the wall should you place the foot of a 10-foot
ladder? Round to the nearest inch.

12. Example 6
What if...? According to the recommended safety ratio of 4:1, how high will a 30-foot ladder reach when placed against a wall? Round to the nearest inch.

13. A Pythagorean triple is a set of three nonzero whole numbers a, b, and c such that a2 + b2 = c2

14. Example 7: Identifying Pythagorean Triples
Find the missing side length. Tell if the side lengths form a Pythagorean triple. Explain.

15. Example 8: Identifying Pythagorean Triples
Find the missing side length. Tell if the side lengths form a Pythagorean triple. Explain.

16. Example 9
Find the missing side length. Tell if the side lengths form a Pythagorean triple. Explain.

17. Example 10
Find the missing side length. Tell if the side lengths form a Pythagorean triple. Explain.

18. Example 11
Find the missing side length. Tell if the side lengths form a Pythagorean triple. Explain.

19. Example 12
Find the missing side length. Tell if the side lengths form a Pythagorean triple. Explain.

20. The converse of the Pythagorean Theorem gives you a way to tell if a triangle is a right triangle when you know the side lengths.

21. You can also use side lengths to classify a triangle as acute or obtuse.

22. To understand why the Pythagorean inequalities are true, consider ∆ABC.

23. By the Triangle Inequality Theorem, the sum of any two side lengths of a triangle is greater
than the third side length.
Remember!

24. Example 13: Classifying Triangles
Tell if the measures can be the side lengths of a triangle. If so, classify the triangle as acute, obtuse, or right.
5, 7, 10

25. Example 14: Classifying Triangles
Tell if the measures can be the side lengths of a triangle. If so, classify the triangle as acute, obtuse, or right.
5, 8, 17

26. Example 15
Tell if the measures can be the side lengths of a triangle. If so, classify the triangle as acute, obtuse, or right.
7, 12, 16

27. Example 16
Tell if the measures can be the side lengths of a triangle. If so, classify the triangle as acute, obtuse, or right.
11, 18, 34

28. Example 17
Tell if the measures can be the side lengths of a triangle. If so, classify the triangle as acute, obtuse, or right.
3.8, 4.1, 5.2

30. Lesson Quiz: Part I
1. Find the value of x.
2. An entertainment center is 52 in. wide and 40 in. high. Will a TV with a 60 in. diagonal fit in it? Explain. 12

31. Lesson Quiz: Part II
3. Find the missing side length. Tell if the side lengths form a Pythagorean triple. Explain.
4. Tell if the measures 7, 11, and 15 can be the side lengths of a triangle. If so, classify the triangle as acute, obtuse, or right.
13; yes; the side lengths are nonzero whole numbers that satisfy Pythagorean’s Theorem.
yes; obtuse