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Chapter 7, continued AC CB AB AB 37. Prove: } 5 } , } 5 } DB AC AD CB 2. By the Base Angles Theorem and the Corollary to the Statements 1. n ABC is a right triangle. } } hypotenuse 5 leg + Ï 2 1. Given } 2. CD > AB 2. Given 3. n ABC , nCBD 3. Theorem 7.5 CB AB 5} 4. } DB CB 4. Definition of similar triangles 5. n ABC , n ACD 5. Theorem 7.5 } y 5 Ï4 y52 3. By the Base Angles Theorem and the Corollary to the Triangle Sum Theorem, the two triangles are 458-458-908 triangles. } hypotenuse 5 leg + Ï 2 6. Definition of similar triangles AC AB 6. } 5} AD AC } d 5 8Ï 2 ø 11.31 } 4. hypotenuse 5 leg + Ï 2 } 38. a. a 5 10, b 5 15 6 5 x + Ï2 2(10)(15) (10 1 15) 2ab a1b 300 25 6 } 5 } 5 } 5 12 } } 5 x Ï2 } The harmonic mean of 10 and 15 is 12. Ï2 6 } } + } } 5 x Ï2 Ï2 b. a 5 6, b 5 14 2(6)(14) 6 1 14 2ab a1b } 3Ï 2 5 x 168 20 } 5 } 5 } 5 8.4 } The length of the hypotenuse is 3Ï2 . } The harmonic mean of 6 and 14 is 8.4. 5. longer leg 5 shorter leg + Ï 3 } c. Strings whose lengths have the ratio 4 : 6 :12 will have x53 2(4k)(12k) will sound harmonious if 6k 5 } . 4k 1 12k } x 5 Ï3 + Ï3 lengths 4k, 6k, and 12k, for any constant k. The strings 6. The equilateral triangle has an altitude that forms the longer leg of two 308-608-908 triangles. 2(4k)(12k) 96k 2 } 5 } 5 6k 16k 4k 1 12k } longer leg 5 shorter leg + Ï 3 So, 6k is the harmonic mean of 4k and 12k, and the strings will sound harmonious. Mixed Review for TAKS } h 5 2Ï 3 ø 3.46 7. h 14 ft 308 39. A; Cost Number of color + of one 1 color copies copy 6 + x 1 10 } y 5 Ï2 + Ï2 + x 1 Cost of Number Total of black + one black 5 cost and white and white copy copies 16 + y 5 1.22 8 + y 5 1.66 Lesson 7.4 7.4 Guided Practice (pp. 458–460) 1. By the Base Angles Theorem and the Corollary to the Triangle Sum Theorem, the triangle is a 458-458-908 triangle. } hypotenuse 5 leg + Ï 2 } } 2Ï 2 5 x + Ï 2 25x hypotenuse 5 2 + shorter leg 14 5 2 + h 75h The height of the body of the dump truck is 7 feet. 8. In a 308-608-908 triangle, the shorter side of the triangle is opposite the 308 angle. The longer side of the triangle is opposite the 608 angle. 7.4 Exercises (pp. 461–464) Skill Practice 1. A triangle with two congruent sides and a right angle is called an isosceles right triangle. 2. The Corollary to the Triangle Sum Theorem requires that the acute angles of a right triangle are complementary. Because the triangle is isosceles, its base angles are congruent. Half of 908 is 458, so each of the acute angles measures 458. } 3. hypotenuse 5 leg + Ï 2 } x 5 7Ï 2 204 Geometry Worked-Out Solution Key Copyright © by McDougal Littell, a division of Houghton Mifflin Company. } Triangle Sum Theorem, the triangle is 458-458-908 triangle. Reasons Chapter 7, continued } 4. hypotenuse 5 leg + Ï 2 } } 5. hypotenuse 5 leg + Ï 2 } } x 5 5Ï2 + Ï2 } 12. hypotenuse 5 2 + shorter leg 3Ï 2 5 x + Ï 2 x 5 5 + 2 5 10 f f 5 2 + d l d 5 }2 35x } longer leg 5 shorter leg + Ï 3 6. C; } } hypotenuse 5 leg + Ï 2 } } eÏ 3 Ï3 Ï3 e Ï3 e 5 d + Ï3 l d 5 } } + } } 5 } 3 } 7 5 AC + Ï 2 7 } } 5 AC Ï2 } 7Ï 2 } 5 AC } } 8Ï 3 + Ï3 3 14 2 }57 }58 d 5 e 5Ï 3 7Ï 3 8Ï 3 f 2 + 5 5 10 14 2 + 8 5 16 } } } 2 } 7. hypotenuse 5 leg + Ï 2 } } 2Ï 2 5 xÏ 2 } 25x The corner triangles have leg lengths of 2 inches. The overall side length of the tile is 2 + 2 5 4 inches. } 5 9Ï 3 e 9Ï3 + Ï3 5 27 f 18Ï3 8. hypotenuse 5 2 + shorter leg y52+9 y 5 18 longer leg 5 shorter leg + Ï 3 } } 15 x5} + Ï3 2 } 3Ï 3 5 x Ï 3 } 15Ï3 35x x5} 2 y 5 2(3) 5 6 Copyright © by McDougal Littell, a division of Houghton Mifflin Company. } 15 2 longer leg 5 shorter leg + Ï3 } 14. hypotenuse 5 leg + Ï 2 10. hypotenuse 5 2 + shorter leg } } Ï6 5 mÏ2 } 12Ï 3 5 2y } Ï6 } 6Ï 3 5 y } } 5 m Ï2 } } longer leg 5 shorter leg + Ï3 } Ï3 5 m } } x 5 6Ï 3 + Ï 3 n 5 m 5 Ï3 x 5 6(3) 15. hypotenuse 5 2 + shorter leg x 5 18 24 5 2p 11. a 5 b 12 5 p } hypotenuse 5 leg + Ï 2 } longer leg 5 shorter leg + Ï 3 } } c 5 aÏ2 q 5 p + Ï3 } } a 7 11 } 10 Ï2 } } + } } 5 5Ï 2 Ï2 Ï2 b 7 11 5Ï 2 } } } 2 + 4Ï3 5 8Ï 3 } y 5 2x } } 12 }5y 9. hypotenuse 5 2 + shorter leg 7Ï 2 11Ï 2 } 15 5 2y } x 5 9Ï 3 c } } } 5 4Ï 3 13. hypotenuse 5 2 + shorter leg } longer leg 5 shorter leg + Ï3 } } 12Ï3 3 } 18Ï 3 2 d 10 q 5 12Ï 3 } 6 Ï5 6 Ï5 16. The altitude s forms the longer leg of two 308-608-908 triangles. } } } } } 6Ï2 Ï5 + Ï2 5 Ï10 hypotenuse 5 2 + shorter leg r 5 21 } 22 18 r 5 18 } longer leg 5 shorter leg + Ï 3 } s 5 9Ï 3 Geometry Worked-Out Solution Key 205 Chapter 7, 17. continued 22. Abigail’s method does work. 3 } t longer leg 5 shorter leg + Ï 3 458 } 9 5 xÏ 3 4 } } } 9Ï 3 5 x + 3 4 } u 3Ï 3 5 x The triangle formed is a 458-458-908 triangle, so each leg has a length of 4. u541357 Her method is algebraically correct, so the equation simplifies to the same answer found in Example 5. 23. } hypotenuse 5 leg + Ï 2 308 608 } f g t 5 4Ï2 10 } longer leg 5 shorter leg + Ï 3 } } longer leg 5 shorter leg + Ï 3 } } 9Ï 3 5 eÏ 3 10 5 gÏ 3 95e } 10 Ï3 } } + } } 5 g Ï3 Ï3 } 10Ï3 }5g 3 hypotenuse 5 2 + shorter leg f 5 2(9) f 5 18 hypotenuse 5 2 + shorter leg The lower triangle is a 458-458-908 triangle. } 1 10Ï3 2 } f52 } 3 hypotenuse 5 leg + Ï 2 } f 5 gÏ2 } 20Ï3 } f5} 3 18 5 gÏ2 18 24. } } 5 g Ï2 } 18 Ï 2 } } + } } 5 g Ï2 Ï2 y x 608 308 1508 4 2 } 9Ï 2 5 g } 4Ï2 5 2x 5 5Ï3 19. C; }, }, 10 2 2 } 2Ï 2 5 x hypotenuse 0 2 + shorter leg } longer leg 5 shorter leg + Ï 3 } 5 y 5 x + Ï3 10 0 2 + }2 } } y 5 2Ï 6 20. The formula for the longer leg was used instead of the 25. 308 hypotenuse formula. The correct solution is: 608 x 8 hypotenuse 5 2 + shorter leg 5 2 + 7 5 14 308 14 608 y First triangle: 308 hypotenuse 5 2 + shorter leg 8 5 2x 21. The length of the hypotenuse was incorrectly calculated } } } } } as leg + leg + Ï 2 5 Ï 5 + Ï5 + Ï 2 5 5Ï2 . The correct solution is: } } } } hypotenuse 5 leg + Ï 2 5 Ï 5 + Ï 2 5 Ï 10 45x Second triangle: } longer leg 5 shorter leg + Ï 3 } 10 458 5 x 5 yÏ 3 } 4 5 yÏ 3 4 Ï3 } } 5 y } 4Ï3 3 }5y 206 } y 5 2Ï 2 + Ï 3 10 Þ 5 Geometry Worked-Out Solution Key Copyright © by McDougal Littell, a division of Houghton Mifflin Company. hypotenuse 5 2 + shorter leg } 5 608 308 18. The upper triangle is a 308-608-908 triangle. 7 } 9Ï3 5 xÏ3 + Ï3 458 Chapter 7, continued }}} 26. CB 5 Ï (3 2 (23))2 1 (21 2 (21))2 } hypotenuse 5 2 + shorter leg 28. } 5 Ï 62 1 02 5 Ï 36 5 6 h ft 608 284 ft hypotenuse 5 2 + shorter leg 284 5 2 + h 142 5 h 308 6 5 2AB } 458 284 5 h + Ï 2 284 ft h ft 3 5 AB 284 } } } 5 h Ï2 458 longer leg 5 shorter leg + Ï 3 } 142Ï2 5 h } AC 5 AB + Ï 3 hypotenuse 5 2 + shorter leg } AC 5 3Ï3 284 5 2 + s Let (x, y) represent the coordinates of A. h ft 308 284 ft }} AB 5 Ï(x 2 3)2 1 ( y 2 (21))2 142 5 s 3 5 Ï(x 2 3) 1 ( y 1 1) 2 2 608 } h 5 142Ï3 9 5 (x 2 3)2 1 ( y 1 1)2 h ø 246 9 2 (x 2 3) 5 ( y 1 1) 2 2 When the angle is 308, the seagull rises 142 feet; when the angle is 458, the seagull rises about 200 feet 10 inches; when the angle is 608, the seagull rises about 246 feet. }}} AC 5 Ï(x 2 (23))2 1 ( y 2 (21))2 }} 3Ï3 5 Ï(x 1 3)2 1 ( y 1 1)2 27 5 (x 1 3)2 1 ( y 1 1)2 29. You could show that all isosceles right triangles are 27 2 (x 1 3)2 5 (y 1 1)2 similar to each other by showing that the corresponding angles are congruent. They are all 458-458-908 triangles. 9 2 (x 2 3)2 5 27 2 (x 1 3)2 9 2 x 2 1 6x 2 9 5 27 2 x 2 2 6x 2 9 You could also show that the corresponding side lengths are always proportional, because in an isosceles }right triangle, the side lengths are always x, x, and xÏ2 . } } For example, let 1, 1, Ï2 , and 2, 2, 2Ï 2 , be the side lengths of two isosceles right triangles. The ratios of 12x 5 18 3 x 5 }2 9 2 1 }2 2 3 2 5 (y 1 1)2 2 Copyright © by McDougal Littell, a division of Houghton Mifflin Company. 3 2 } 1 2 9 2Ï2 } } 5 2. Ï2 30. Because nDEF is a 458-458-908 triangle, DF 5 FE. By the Pythagorean Theorem, DF 2 1 FE 2 5 DE 2. This 2 equation can be written as 2DF 5 DE 2 or 2FE 2 5 DE 2. } Ï By the Property of Squares, 2 DF 5 DE and } } Ï 2 FE 5 DE. So, the hypotenuse is equal to Ï 2 times the length of one leg of the 458-458-908 triangle. 9 2 }4 5 y 2 1 2y 1 1 23 0 5 y 2 1 2y 2 } 4 0 5 4y 2 1 8y 2 23 }} 28 6 Ï82 2 4(4)(223) y 5 }} 2(4) } 28 6 Ï 432 5} 8 } 3Ï 3 5 21 6 } 2 Point A lies in the first quadrant, so its y-coordinate is positive. } 1 2 corresponding side lengths are }1 5 2, }1 5 2, and 3 2 9 2 2}2 5 y 2 1 2y 1 1 3Ï 3 3 A }2 , 21 1 } 2 } longer leg 5 shorter leg + Ï3 }} } } hypotenuse 5 leg + Ï2 CB 5 2AB 2 Problem Solving 31. 20 in. h 608 608 20 in. h 308 608 20 in. 608 10 in. 20 in. The height h divides the equilateral triangle into two 308-608-908 triangles. } longer leg 5 shorter leg + Ï3 } h 5 10Ï3 ø 17.3 The height of the equilateral triangle is about 17.3 inches. 27. hypotenuse 5 2 + shorter leg 11 5 2h 11 2 }5h 5.5 5 h The height of the ramp is 5 feet 6 inches. Geometry Worked-Out Solution Key 207 Chapter 7, This process can be duplicated to find the unknown lengths of the remaining right triangles. K 608 x 308 L t 2 5 12 1 s 2 x t 5 1 1 (Ï3 ) M t2 5 1 1 3 Because n JML > n JKL, m M 5 m K 5 608. So, all three angles of n JKM measure 608, and the triangle is equilateral. So, all of its side lengths are x 1 x 5 2x. It is given that the shorter leg of n JKL is x. So, n JKL’s hypotenuse is two times the length of its shorter side. By the Pythagorean Theorem, JL2 1 x 2 5 (2x)2, } and JL2 5 4x 2 2 x 2 5 3x 2. This simplifies to}JL 5 Ï3 x, showing that the longer leg is equal to Ï3 times the length of the shorter leg. 33. a. The large orange triangles are 458-458-908 triangles, because they are isosceles right triangles. The smaller blue triangles are also 458-458-908 triangles, because the 458 angles of the orange triangle are complementary with the acute angles of the blue triangle. v2 5 1 1 5 w2 5 1 1 6 v2 5 6 w2 5 7 308-608-908 triangle. It is the only one whose side lengths satisfy the 308-608-908 Triangle Theorem. 35. a. Q 8 b. QR > SR, QT > ST, and TR is shared by the two triangles so nRQT > nRST by the Side-Side-Side Congruence Postulate. c. RT is longer than QS. ZR is the longer leg of a 308-608-908 triangle, so ZR > ZS. From part (b), nRQT > nRST, so QTR > STR. Because m QTS 5 908, m QTR 5 m STR 5 458. Because nQTS is an isosceles right triangle, its base angles measure 458. So, nQZT and nTZS are congruent right isosceles triangles, and QZ 5 TZ 5 ZS. So, ZR 1 TZ > ZS 1 QZ, and RT > QS. } hypotenuse 5 leg + Ï 2 } } 3Ï 2 } 5 y + Ï2 2 3 2 }5y 458 1.5 5 y The square of fabric for the small blue triangles should be 1.5 inches by 1.5 inches. 34. a. The first triangle is a 458-458-908 triangle, because the legs are both 1. } hypotenuse 5 leg + Ï 2 } r 5 1 + Ï2 } r 5 Ï2 The } second triangle is a right triangle with legs 1 and r 5 Ï 2 . Using the Pythagorean Theorem, s 2 5 12 1 r 2 } s 2 5 1 1 (Ï 2 )2 s2 5 1 1 2 R S The square of fabric for the large orange triangles should be about 2.12 inches by 2.12 inches. 3 2 2 Z T 8 } 458 Mixed Review for TAKS 36. B; Choice A: 142 0 82 1 122 196 0 64 1 144 196 Þ 208 The triangle is not a right triangle. Choice B: 292 0 202 1 212 841 0 400 1 441 841 5 841 The triangle is a right triangle. Choice C: 162 0 92 1 122 256 0 81 1 144 256 Þ 225 The triangle is not a right triangle. 2 } s 5 Ï3 . Geometry Worked-Out Solution Key } w 5 Ï7 } 3 y } } c. The third triangle, with sides 1, Ï 3 , 2, is the only 2.12 ø x 208 w 2 5 12 1 (Ï6 )2 first one, because it is the only one whose legs are equal in length. } s 53 v 2 5 1 1 (Ï 5 )2 b. The only triangle that is a 458-458-908 triangle is the } } 5 x Ï2 3Ï 2 }5x 2 y w 2 5 12 1 v 2 608 Ï2 3 } } + } } 5 x Ï2 Ï2 c. v 2 5 12 1 u 2 v 5 Ï6 } 458 } u 5 Ï5 } 3 5 x + Ï2 3 x u2 5 5 t52 } 458 u 2 5 1 1 22 t 54 hypotenuse 5 leg + Ï 2 x u 2 5 12 1 t 2 2 2 Construct n JML congruent to n JKL. Because they are congruent, m KJL 5 m LJM 5 308, so m KJM 5 m KJL 1 m LJM 5 308 1 308 5 608. b. } 2 Copyright © by McDougal Littell, a division of Houghton Mifflin Company. 32. continued Chapter 7, continued } Choice D: 252 0 102 1 242 5. longer leg 5 shorter leg + Ï 3 } 3Ï2 5 aÏ3 625 Þ 676 3Ï2 } } 5 a } The triangle is not a right triangle. } The triangle given in Choice B, a triangle with lengths 20 inches, 21 inches, and 29 inches, is a right triangle. Quiz 7.3–7.4 (p. 464) 1. Ï3 } 3Ï2 Ï3 } } + } } 5 a Ï3 Ï3 } Ï6 5 a hypotenuse 5 2 + shorter leg b 5 2a C B 10 6 B A D A D BC CD }5} BC 2 5 CD 2 1 BD 2 102 5 6 2 1 BD 2 64 5 BD 40 in. 402 5 152 1 h2 15 in. 30 in. 1600 5 225 1 h2 h 40 in. 1375 5 h2 1 Area 5 }2(base)(height) ø }2(30)(37.08) 5 556.2 in.2 8 5 BD Larger sign: 64 in. 642 5 242 1 h2 24 in. 4096 5 576 1 h2 8 6 }5} h 48 in. 3520 5 h2 6 + AD 5 8 + 8 64 in. 59.33 ø h 64 AD 5 } 6 Copyright © by McDougal Littell, a division of Houghton Mifflin Company. 1. D; 1 2 BD AD }5} CD BD 1 1 Area 5 }2(base)(height) ø }2(48)(59.33) 5 1423.92 in.2 32 Ratio of areas: 556.2 : 1423.92 ø 0.3906 : 1 AD 5 } ø 10.67 3 AB BD Mixed Review for TEKS (p. 465) B 37.08 ø h 100 5 36 1 BD 2 AD 8 10 Smaller sign: BC is the geometric mean of AC and CD. 2. } b 5 2Ï 6 C AC BC } 625 0 100 1 576 BC CD }5} 10 AB }5} 6 8 6 + AB 5 8 + 10 3:4 5 Choice B: 5:8 5 0.625 : 1 Choice C: 9 : 16 5 0.5625 : 1 Choice D: 25 : 64 ø 0.3906 : 1 0.75 : 1 The ratio of the area of the smaller sign to the area of the larger sign is about 25 : 64. 6 + AB 5 80 80 Choice A: 40 5} ø 13.3 AB 5 } 6 3 } 3. hypotenuse 5 leg + Ï 2 } x 5 8Ï2 } 10 5 y + Ï 2 10 } } 5 y Ï2 } 10Ï 2 }5y 2 Using the formula d 5 r + t (Distance 5 Rate + Time), t 5 1.5 h. Sandra: } 4. hypotenuse 5 Ï 2 2. H; Tina: r 5 5 mi/h r 5 4 mi/h d 5 (5)(1.5) 5 7.5 mi d 5 (4)(1.5) 5 6 mi Because Sandra runs west and Tina runs south, their paths are legs of a right triangle. N 7.5 mi } W 5Ï 2 5 y E S c 6 mi c2 5 62 1 7.52 5 36 1 56.25 5 92.25 } c 5 Ï 92.25 ø 9.6 At 10:30 A.M., Sandra and Tina are about 9.6 miles apart. Geometry Worked-Out Solution Key 209 Chapter 7, continued 3. C; Step 3 Because 10 < x < 14, x is the length of the longest side of the triangle. The sum of the squares of the lengths of the other two sides is 82 1 62 5 64 1 36 5 100. Because 10 < x < 14, 100 < x 2 < 196, so the square of the length of the longest side is greater than the sum of the squares of the lengths of the other two sides. So, by Theorem 7.4, the triangle is obtuse. Therefore, 1 is obtuse. 4. F; The triangle formed by the pushpins is not equilateral because the 3 sides formed are not congruent. ? 1192 1 2082 ? 14,161 1 43,264 50,625 50,625 < 57,425 Because the square of the length of the longest side of the triangle is less than the sum of the squares of the lengths of the other 2 sides, by Theorem 7.3 the triangle formed is acute. 5. C; n ABC , n ADE. The two triangles are similar because their corresponding angles are congruent. Step 4 Sample answer: The ratio of the lengths of the legs in a right triangle is constant for a given angle measure; answers will vary. 7.5 Guided Practice (pp. 467–468) opp. J 3 24 1. tan J 5 } 5 } 5 } 5 0.75 32 4 adj. to J opp. K 32 4 5} 5 }3 ø 1.3333 tan K 5 } 24 adj. to K opp. J 8 2. tan J 5 } 5 } ø 0.5333 15 adj. to J opp. K 15 tan K 5 } 5} 5 1.875 8 adj. to K opp. 3. tan 618 5 } adj. x 2 5 32 1 22 22 tan 618 5 } x x 5914 2 x + tan 618 5 22 x 2 5 13 } x 5 Ï13 ø 3.6 22 tan 618 x5} The length of the plywood is about 3.6 feet. 6. 51; 22 xø} ø 12.2 1.8040 N 24 Treasure (24, 45) Stump opp. tan 568 5 } adj. 4. x (30, 20) 45 W DE BC tan 568 5 } 13 (24, 20) (0, 0) (30, 0) 13 + tan 568 5 x E 13(1.4826) ø x S If the stump is at point (0, 0) then the hidden treasure is at point (24, 45). The shortest distance from the treasure } } to the stump is Ï 452 1 242 5 Ï2601 5 51 paces. 19.3 ø x 5. 608 5 5 3 Lesson 7.5 } longer leg 5 shorter leg + Ï 3 } Activity (p. 466) x 5 5Ï 3 Step 1 opp. } 5Ï3 } tan 608 5 } 5} 5 Ï3 5 adj. Check student’s work. Step 2 7.5 Exercises (pp. 469–472) Sample answer: 210 Triangle Adjacent Leg Opposite Leg }} n ABC 5 cm 2.9 cm 0.58 n ADE 10 cm 5.8 cm 0.58 n AFG 15 cm 8.7 cm 0.58 Opposite Leg Adjacent Leg Skill Practice 1. The tangent ratio compares the length of the leg opposite the angle to the length of the leg adjacent to the angle. 2. All right triangles with an acute angle measuring n8 will Geometry Worked-Out Solution Key have the same ratio of the leg opposite the angle to the leg adjacent to the angle because tangent n8 is a constant. So, the triangles must be similar. Copyright © by McDougal Littell, a division of Houghton Mifflin Company. 2252 AC BC 5} and } 5} are true because The proportions } AE AE DE AC