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CHAPTER Solutions Key
6 Polygons and Quadrilaterals
ARE YOU READY? PAGE 377 19. F (counterexample: △ with side lengths 5, 6, 10);
if a triangle is an acute triangle, then it is a scalene
1. F 2. B triangle; F (counterexample: any equilateral
3. A 4. D triangle).
5. E
6. Use △ Sum Thm. 6-1 PROPERTIES AND ATTRIBUTES OF
x ° + 42° + 32° = 180° POLYGONS, PAGES 382–388
x ° = 180° - 42° - 32° CHECK IT OUT!
x ° = 106° 1a. not a polygon b. polygon, nonagon
7. Use △ Sum Thm. c. not a polygon
x ° + 53° + 90° = 180°
x ° = 180° - 53° - 90° 2a. regular, convex b. irregular, concave
x ° = 37° 3a. Think: Use Polygon ∠ Sum Thm.
8. Use △ Sum Thm. (n - 2)180°
x ° + x ° + 32° = 180° (15 - 2)180°
2 x ° = 180° - 34° 2340°
2 x ° = 146° b. (10 - 2)180° = 1440°
x ° = 73° m∠1 + m∠2 + … + m∠10 = 1440°
9. Use △ Sum Thm. 10m∠1 = 1440°
2 x °
+ x ° + 57° = 180° m∠1 = 144°
3 x ° = 180° - 57° 4a. Think: Use Polygon Ext. ∠ Sum Thm.
3 x ° = 123° m∠1 + m∠2 + … + m∠12 = 360°
x ° = 41° 12m∠1 = 360°
10. By Lin. Pair Thm., 11. By Alt. Ext. Thm., m∠1 = 30°
m∠1 + 56 = 180 m∠2 = 101° b. 4r + 7r + 5r + 8r = 360
m∠1 = 124° By Lin. Pair Thm., 24r = 360
By Vert. Thm., m∠1 + m∠2 = 180 r = 15
m∠2 = 56° m∠1 + 101 = 180
By Corr. Post., m∠1 = 79° 5. By Polygon Ext. ∠ Sum Thm., sum of ext. ∠
m∠3 = m∠1 = 124° Since ℓ ⊥ m, m n measures is 360°. Think: There are 8 ext. , so
By Alt. Int. Thm., → ℓ ⊥ n, divide sum by 8.
360°
m∠4 = 56° m∠3 = m∠4 = 90°. _
m(ext. ∠) =
= 45°
12. By Same-Side Int. Thm., 8
3x + 2x = 180 THINK AND DISCUSS
5x = 180 1. Possible answers:
x = 36 Concave pentagon Convex pentagon
By Lin. Pair
Thm.,
m
∠1 + 3(36) = 180
m∠1 + 108 = 180
m∠1 = 72°
By Corr. Post.,
m∠2 = 3(36) = 108° A concave polygon seems to “cave in” or have a
13. 45°-45°-90° △ 14. 30°-60°-90° △ dent. A convex polygon does not have a dent.
√ √ 2. Since polygon is not regular, you cannot assume
( )
x = 11 2 2 14 = 2x
= 11(2) = 22 x = 7 that each of the ext. has the same measure.
15. 45°-45°-90° △ 16. 30°-60°-90° △ 3. )NTERIOR!NGLES %XTERIOR!NGLES
√
x = 3
2 x = 2(8) = 16
3UMOF!NGLE-EASURES
n
17. T (Lin. Pair Thm.); if 2 are supp., then they form a
n
lin. pair; F (counterexample: any supp. but non-adj. /NE!NGLE-EASURE
nn
pair of ).
18. F (counterexample: a pair of with measure 30°);
if 2 are rt , then they are ; T (Rt. ∠ Thm.).
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25. 9m(ext. ∠) = 360
EXERCISES
GUIDED PRACTICE m(ext. ∠) = 40°
1. Possible answer: If a polygon is equil., all its sides 26. 5a + 4a + 10a + 3a + 8a = 360
are , but all its are not necessarily . For a 30a = 360
polygon to be regular, all its sides must be , and a = 12
all its must be . 27. 6m∠JKM = (6 - 2)180 28. 6m∠MKL = 360
2. polygon, decagon 3. not a polygon 6m∠JKM = 720 m∠MKL = 60°
m∠JKM = 120°
4. polygon, quadrilateral 5. not a polygon 29. x + x - 3 + 1
10 + 130 = (4 - 2)180
6. regular, convex 7. irregular, concave 2x
+ 237 = 360
8. irregular, convex 2x = 123
9. Think: Use Polygon ∠ Sum Thm. x = 61.5
(5 - 2)180° = 540° 30. 2(90) + 2x + 2(x + 22) = (6 - 2)180
3z + 4z + 5z + 3z + 5z = 540 4x + 224 = 720
20z = 540 4x = 496
z = 27 x = 124
m∠A = m∠D = 3(27) = 81° 31. 5x = 360°
m∠B = 4(27) = 108° x = 72°
m∠C = m∠E = 5(27) = 135° 32. m∠ = m(ext. ∠)
10. ∠ Sum Thm. n(m∠) = n(m(ext. ∠))
Think: Use Polygon
(12 - 2)180° = 1800° (n - 2)180 = 360
m∠1 + m∠2 + … + m∠12 = 1800° 180n = 720
12m∠1 = 1800° n = 4
m∠1 = 150° 33. m∠ = 4m(ext. ∠)
11. Think: Use Polygon ∠ Sum Thm. n(m∠) = 4n(m(ext. ∠))
(n - 2)180° (n - 2)180 = 4(360)
(20 - 2)180° 180n = 1800
3240° n = 10
1
12. Think: Use Polygon Ext. ∠ Sum Thm. _
34. m(ext. ∠) =
m∠
4y + 2y + 6y + 4y = 360 8
16y = 360 8n(m(ext. ∠)) = n(m∠)
y = 22.5 8(360) = (n - 2)180
3240 = 180n
13. Think: Use Polygon Ext. ∠ Sum Thm. n = 18
m∠1 + m∠2 + … + m∠5 = 360° 35. (n - 2)180 = 540 36. (n - 2)180 = 900
5m∠1 = 360° n - 2 = 3 n - 2 = 5
m∠1 = 72° n = 5 n = 7
14. pentagon pentagon heptagon
15. By Sum Thm., sum of ∠ measures is
Polygon ∠ 37. (n - 2)180 = 1800 38. (n - 2)180 = 2520
(5 - 2)180 = 540°. Think: m∠Q = m∠S by def. of . n - 2 = 10 n - 2 = 14
m∠P + m∠Q + m∠R + m∠S + m∠T = 540 n = 12 n = 16
90 + m∠S + 90 + m∠S + 90 = 540 dodecagon 16-gon
2m∠S = 270 39. 360 = n(120) 40. 360 = n(72)
m∠Q = m∠S = 135° n = 3 n = 5
PRACTICE AND PROBLEM SOLVING m ∠ = 180 - 120 = 60° m ∠ = 180 - 72 = 108°
16. polygon, hexagon 17. not a polygon 41. 360 = n(36) 42. 360 = n(24)
18. polygon, quadrilateral 19. irregular, concave n = 10 n = 15
20. regular convex 21. irregular, convex m ∠ = 180 - 36 = 144° m ∠ = 180 - 24 = 156°
22. 2n + 6n + 2n + 5n = (4 - 2)180 43. A; possible answer: this is not a plane figure, so it
15n = 360 cannot be a polygon.
n = 24
m∠R = m∠T = 2(24) = 48°
m∠S = 6(24) = 144°
m∠V = 5(24) = 120°
23. 18m∠ = (18 - 2)180 24. (7 - 2)180 = 900°
18m∠ = 2880
m∠ = 160°
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44. C y CHALLENGE AND EXTEND
x 56. ∠ measures are a, a + 4, …, a + 16, where a is a
B D multiple of 4.
a + a + 4 + … + a + 16 = (5 - 2)180
5a + 40 = 540
5a = 500
A E a = 100
Check students’ estimates; possible answer: ∠ measures are 100°, 104°, 108°, 112°, and 116°.
−− −− −− −−
57.
pentagon is not equiangular; m∠A = 100°; PQ ST , QR RS , and ∠Q ∠S. So by SAS,
−− −−
m∠B = 113°; m∠C = 113°; m∠D = 101°; △PRQ △SRT. By CPCTC, PR RT , so △PRT
m∠E = 113°; yes, pentagon is not equiangular. is isosc. By Isosc. △ Thm., ∠RTP ∠RPT, so
45a. heptagon b. (7 - 2)180 = 900° m∠RTP = m∠RPT = z°.
By △ Sum Thm.,
c. m∠A + m∠B + m∠C + m∠D 2z + y = 180 (1)
+ m∠E + m∠F + m∠G = 900 By CPCTC and Isosc. △ Thm.,
95 + 125 + m∠F + 130 ∠PRQ ∠SRT ∠ QPR ∠RTS
+ 130 + m∠F + m∠F = 900 m∠PRQ = m∠SRT = m∠QPR = m∠RTS = x°
3m∠F + 480 = 900 Since PQRST is reg., Subtr. (3) from (1):
3m∠F = 420 5m∠QRS = (5 - 2)180 z = 180 - 108 = 72°
m∠F = 140° 5(2x + y) = 540 Subst: in (3):
46. Let n be number of sides and s (= 7.5) be side length. 2x + y = 108 (2) y + 72 = 108
P = ns 5m∠PTS = (5 - 2)180 y = 36°
45 = n(7.5) 5(y + z) = 540 Subst. in (2):
n = 6 y + z = 108 (3) 2x + 36 = 108
Polygon is a (regular) hexagon. 2x = 72
48. Possible answer: x = 36°
47. −− −− −−
58.
KA
EF
LC . By Alt. Int. Thm., ∠BLC ext. ∠A
and ∠CLD ext. ∠E 360
_
m∠ALC = m∠CLE =
= 36°
10
m∠BLD = m∠BLC + m∠CLD = 72°
49. Possible answer: 50. Possible answer: 59. Yes, if you allow for ∠ measures greater than 180°.
m∠A + m∠B + m∠C + m∠D + m∠E + m∠F = 720°
C
B
51. The figure has 6 sides, so it is a hexagon. The 6 A D
sides are , so the hexagon is equilateral. The 6
are , so the hexagon is equiangular. Since the E
hexagon is equilateral and equiangular, it is regular. F
No diagonal contains pts. in the interior, so it is
convex. SPIRAL REVIEW
2 2
52. As number of sides increases, isosc. formed by 60. x + 3x - 10 = 0 61. x - x - 12 = 0
each side become thinner, and dists. from any pt. (x + 5)(x - 2) = 0 (x - 4)(x + 3) = 0
on base of each triangle to its apex approach same x = -5 or x = 2 x = 4 or x = -3
value. For a circle, each pt. is the same dist. from 2 63. x + 4 > 4
62. x - 12x = -35
center. So polygon begins to resemble a circle. 2 x > 0
x - 12x + 35 = 0
TEST PREP (x - 7)(x - 5) = 0 4 + 4 > x
x = 7 or x = 5 8 > x
53. A 54. H 0 < x < 8
(16 -2)180 = 2520° 64. Check x + 6 > 12 and 65. Check x + 3 > 7 and
≠ 2880° 6 + 12 > x, since 6 < 12. 3 + 7 > x, since 3 < 7.
55. D x + 6 > 12 x + 3 > 7
49 + 107 + 2m∠D + m∠D = (4 - 2)180 x > 6 x > 4
3m∠D = 204 6 + 12 > x 3 + 7 > x
m∠D = 68° 18 > x 10 > x
m∠C = 2(68) = 136° 6 < x < 18 4 < x < 10
127 Holt McDougal Geometry
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66. c = 2a 67. c = 2a 3.
= 2(6) = 12 10 = 2a 0ROPERTIESOF0ARALLELOGRAMS
a = 5
/PPSIDESȡ /PPSIDESɈ /PPѓɈ #ONSѓSUPP $IAGSBISECT
√ √
b = a 3 = 5 3
EACHOTHER
x
6-2 PROPERTIES OF PARALLELOGRAMS, x
x
PAGES 391–397 x
CHECK IT OUT!
−− −−
1a. KN LM b. ∠NML ∠LKN EXERCISES
KN = LM = 28 in. m∠NML = m∠LKN GUIDED PRACTICE
= 74° 1. Only 1 pair of sides is . By def., a
has 2 pairs of
−−
c. O is mdpt. of LN sides.
1
_
LO = LN 2. Possible answer:
2 −− −− −−
1
_ Q R opp. sides: PQ and RS , QR
= (26) = 13 in. −−
2 and SP ; opp. : ∠P and
−− −− −− −−
b.
2a. EJ JG FJ JH ∠R, ∠Q and ∠S
EJ = JG FJ = JH P S
3w = w + 8 4z - 9 = 2z −− −− −−
3. E is mdpt. of
BD 4. CD AB
2w = 8 2z = 9 BD = 2DE CD = AB = 17.5
w = 4 FH = 2JH = 2(18) = 36
JG = (4) + 8 = 12 = 2(2z) −−
5. E is mdpt. of
= 2(9) = 18 BD
3. Step 1 Graph given pts. BE = DE = 18
y R 6. ∠ABC and ∠BCD are supp.
Step 2 Find slope
−− Q m∠ABC = 180 - m∠BCD
of
PQ by counting units
from P to Q. = 180 - 110 = 70°
Rise from -2 to 4 is 6. 7. ∠ADC ∠ABC 8. ∠DAB BCD
Run from -3 to -1 is 2. x m∠ADC = m∠ABC m∠DAB = m∠BCD
Step 3 Start at S and S
= 70° = 110°
count same # of pts. P −− −−
9. 10. LM = 3(3.5) + 14
Rise of 6 from 0 is 6. JK LM
Run of 2 from 5 is 7. JK = LM = 24.5
−− −− 7 x = 3x + 14
Step 4 Use slope formula to verify that QR PS . 4 x = 14
−− 6 - 4 1
_ _
QR =
slope of = x = 3.5
7 + 1 4 JK = 7(3.5) = 24.5
−− 0 + 2 1
_ _
slope of PS =
=
5 + 3 4 11. ∠L and ∠M are supp. 12. m∠M = 5(27) - 6
Coords. of vertex R are (7, 6). m∠L + m∠M = 180 = 129°
4. Statements Reasons 2z - 3 + 5z - 6 = 180
7z = 189
1. GHJN and JKLM are ▱. 1. Given z = 27
2. ∠N and ∠HJN are supp.; 2.
→ cons. m∠L = 2(27) - 3 = 51°
∠K and ∠MJK are supp. are supp. 13. Step 1 Graph given pts.
3. ∠HJN ∠MJK 3. Vert. Thm. y
4. ∠N ∠K 4. Supps. Thm. Step 2 Find slope F
−− D
of
FG by counting units
from F to G. x
THINK AND DISCUSS Rise from 5 to 0 is -5. H G
1. Measure of opp. ∠ is 71°. Measure of each cons. ∠ Run from -1 to 2 is 3.
is 180 - 71 = 109°. Step 3 Start at D and
2. XY = 21, WZ = 18, and YZ = 18; possible answer: count same # of pts.
since VWXY is a
, opp. sides are , so XY = VW Rise of -5 from 4 is -1.
−−− Run of 3 from -9 is -6. −− −−
= 21.
WY is a diag., and by Thm. 6-2-4, the other Step 4 Use slope formula to verify that DF GH .
diag. bisects it, so WZ = YZ = 36 ÷ 2 = 18. −− 5 - 4 1
__
DF =
slope of =
-1 + 9 8
−− -1 - 0 1
__
slope of GH =
=
-6 - 2 8
Coords. of vertex H are (-6, -1).
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