1. Objectives
Use the Pythagorean Theorem and its converse to solve problems.
Use Pythagorean inequalities to classify triangles.

2. The Pythagorean Theorem is probably the most famous mathematical relationship. As you learned in Lesson 1-6, it 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.

3. Example 1A: Using the Pythagorean Theorem
Find the value of x. Give your answer in simplest radical form.

4. Example 1B: Using the Pythagorean Theorem
Find the value of x. Give your answer in simplest radical form.

5. Check It Out! Example 1c
Find the value of x. Give your answer in simplest radical form.

6. Check It Out! Example 1d
Find the value of x. Give your answer in simplest radical form.

7. Example 2a: 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.

8. Check It Out! Example 2b
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.

9. A set of three nonzero whole numbers a, b, and c such that a2 + b2 = c2 is called a ________________.

10. than the third side length. Remember!
You can also use side lengths to classify a triangle as acute or obtuse. A B C c b a
By the Triangle Inequality Theorem, the sum of any two side lengths of a triangle is greater
than the third side length.
Remember!

11. Example 3A: 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

12. Example 3B: 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

13. Check It Out! Example 3c
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

14. Check It Out! Example 3d
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

15. Check It Out! Example 3e
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