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LESSON 8–2

LESSON 8–2. The Pythagorean Theorem and Its Converse. Five-Minute Check (over Lesson 8–1) TEKS Then/Now New Vocabulary Theorem 8.4: Pythagorean Theorem Proof: Pythagorean Theorem Example 1: Find Missing Measures Using the Pythagorean Theorem Key Concept: Common Pythagorean Triples

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LESSON 8–2

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  1. LESSON 8–2 The Pythagorean Theorem and Its Converse

  2. Five-Minute Check (over Lesson 8–1) TEKS Then/Now New Vocabulary Theorem 8.4: Pythagorean Theorem Proof: Pythagorean Theorem Example 1: Find Missing Measures Using the Pythagorean Theorem Key Concept: Common Pythagorean Triples Example 2: Use a Pythagorean Triple Example 3: Use the Pythagorean Theorem Theorem 8.5: Converse of the Pythagorean Theorem Theorems: Pythagorean Inequality Theorems Example 4: Classify Triangles Lesson Menu

  3. A.2 B.4 C. D. Find the geometric mean between 9 and 13. 5-Minute Check 1

  4. Find the geometric mean between A. B. C. D. 5-Minute Check 2

  5. A.4 B. C.6 D. Find the altitude a. 5-Minute Check 3

  6. Find x, y, and z to the nearest tenth. A.x = 6, y = 8, z = 12 B.x = 7, y = 8.5, z = 15 C.x = 8, y≈ 8.9, z≈ 17.9 D.x = 9, y≈ 10.1, z = 23 5-Minute Check 4

  7. Which is the best estimate for m? A. 9 B. 10.8 C. 12.3 D. 13 5-Minute Check 5

  8. Targeted TEKS G.6(D) Verify theorems about the relationships in triangles, including proof of the Pythagorean Theorem, the sum of interior angles, base angles of isosceles triangles, mid-segments, and medians, and apply these relationships to solve problems. G.9(B) Apply the relationships in special right triangles 30º-60º- 90º and 45º-45º-90º and the Pythagorean theorem, including Pythagorean triples, to solve problems. Mathematical Processes G.1(D), G.1(E) TEKS

  9. You used the Pythagorean Theorem to develop the Distance Formula. • Use the Pythagorean Theorem. • Use the Converse of the Pythagorean Theorem. Then/Now

  10. Pythagorean triple Vocabulary

  11. Concept

  12. Concept

  13. Find Missing Measures Using the Pythagorean Theorem A. Find x. The side opposite the right angle is the hypotenuse, so c = x. a2 + b2 = c2 Pythagorean Theorem 42 + 72 = c2a = 4 and b = 7 Example 1

  14. Answer: Find Missing Measures Using the Pythagorean Theorem 65 = c2 Simplify. Take the positive square root of each side. Example 1

  15. Find Missing Measures Using the Pythagorean Theorem B. Find x. The hypotenuse is 12, so c = 12. a2 + b2 = c2 Pythagorean Theorem x2 + 82 = 122b = 8 and c = 12 Example 1

  16. Answer: Find Missing Measures Using the Pythagorean Theorem x2 + 64 = 144 Simplify. x2 = 80 Subtract 64 from each side. Take the positive square root of each side and simplify. Example 1

  17. A. B. C. D. A. Find x. Example 1A

  18. A. B. C. D. B. Find x. Example 1

  19. Concept

  20. Use a Pythagorean Triple Use a Pythagorean triple to find x. Explain your reasoning. Example 2

  21. ? Check: 242 + 102 = 262Pythagorean Theorem Use a Pythagorean Triple Notice that 24 and 26 are multiples of 2: 24 = 2 ● 12 and 26 = 2 ● 13. Since 5, 12, 13 is a Pythagorean triple, the missing leg length x is 2 ● 5 or 10. Answer: x = 10  676 = 676Simplify. Example 2

  22. Use a Pythagorean triple to find x. A. 10 B. 15 C. 18 D. 24 Example 2

  23. Use the Pythagorean Theorem A 20-foot ladder is placed against a building to reach a window that is 16 feet above the ground. How many feet away from the building is the bottom of the ladder? A 3 B 4 C 12 D 15 Example 3

  24. Use the Pythagorean Theorem Read the Item The distance the ladder is from the house, the height the ladder reaches, and the length of the ladder itself make up the lengths of the sides of a right triangle. You need to find the distance the ladder is from the house, which is a leg of the triangle. Solve the Item Method 1 Use a Pythagorean triple. The length of a leg and the hypotenuse are 16 and 20, respectively. Notice that 16 = 4 ● 4 and 20 = 4 ● 5. Since 3, 4, 5 is a Pythagorean triple, the missing length is 4 ● 3 or 12. The answer is C. Example 3

  25. Use the Pythagorean Theorem Method 2 Use the Pythagorean Theorem. Let the distance the ladder is from the house be x. x2 + 162 = 202 Pythagorean Theorem x2 + 256 = 400 Simplify. x2 = 144 Subtract 256 from each side. x = 12 Take the positive square root of each side. Answer: The answer is C. Example 3

  26. A 10-foot ladder is placed against a building. The base of the ladder is 6 feet from the building. How high does the ladder reach on the building? A. 6 ft B. 8 ft C. 9 ft D. 10 ft Example 3

  27. Concept

  28. Concept

  29. Classify Triangles A. Determine whether 9, 12, and 15 can be the measures of the sides of a triangle. If so, classify the triangle as acute, right, or obtuse. Justify your answer. Step 1 Determine whether the measures can form a triangle using the Triangle Inequality Theorem. 9 + 12 > 15  9 + 15 > 12  12 + 15 > 9  The side lengths 9, 12, and 15 can form a triangle. Example 4

  30. ? c2 = a2 + b2 Compare c2 and a2 + b2. ? 152 = 122 + 92 Substitution Classify Triangles Step 2 Classify the triangle by comparing the square of the longest side to the sum of the squares of the other two sides. 225 = 225 Simplify and compare. Answer:Since c2 = a2 + b2, the triangle is a right triangle. Example 4

  31. Classify Triangles B. Determine whether 10, 11, and 13 can be the measures of the sides of a triangle. If so, classify the triangle as acute, right, or obtuse. Justify your answer. Step 1 Determine whether the measures can form a triangle using the Triangle Inequality Theorem. 10 + 11 > 13  10 + 13 > 11  11 + 13 > 10  The side lengths 10, 11, and 13 can form a triangle. Example 4

  32. ? c2 = a2 + b2 Compare c2 and a2 + b2. ? 132 = 112 + 102 Substitution Classify Triangles Step 2 Classify the triangle by comparing the square of the longest side to the sum of the squares of the other two sides. 169 < 221 Simplify and compare. Answer:Since c2 < a2 + b2, the triangle is acute. Example 4

  33. A. Determine whether the set of numbers 7, 8, and 14 can be the measures of the sides of a triangle. If so, classify the triangle as acute, right, or obtuse. Justify your answer. A. yes, acute B. yes, obtuse C. yes, right D. not a triangle Example 4

  34. B. Determine whether the set of numbers 14, 18, and 33 can be the measures of the sides of a triangle. If so, classify the triangle as acute, right, or obtuse. Justify your answer. A. yes, acute B. yes, obtuse C. yes, right D. not a triangle Example 4

  35. LESSON 8–2 The Pythagorean Theorem and Its Converse

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