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CHAPTER 5
80 GeometryChapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
Think & Discuss (p. 261)
1. Answers may vary.
Sample answer:
At position B, the goalkeeper is closer to both sides ofthe imaginary triangle formed by the goal posts and theopponent. The goal keeper has an equal space to defendto the left and right and so has a greater chance of catch-ing or deflecting a ball shot to either side than she wouldhave at position A or position C.
2. about an opponent could move closer to the goal toincrease the shooting angle.
Skill Review (p. 262)
1. Sample answer:
3.
4.
5.
6. The slope of the line perpendicular to is because
Lesson 5.1
Developing Concepts Activity 5.1 (p. 263)
Exploring the Concept
1.–3. Sample answer
5. m�CMA � 90�
BMA
C
�12 � 2 � �1.
�12BC
� 2��4�2
�0 � 4
�2 � 0m �
y2 � y1
x2 � x1
� 5
� �25
� �9 � 16
� ���3�2 � 42
AB � ��0 � 3�2 � �4 � 0�2
� ��1, 2�� ��22
, 42�M � �0 � ��2�
2,
4 � 02 �
A BM
40�;
Drawing Conclusions
1. CMvxxxy is perpendicular to ABxxx since and
CMvxxxy intersects ABxxx at its midpoint.
2. Sample answers:
3. Sample answer:
The distances from D to the endpoints A and B are equal,the distances from E to the endpoints A and B are equal,the distances from F to the endpoints A and B are equal,and the distances from G to the endpoints A and B areequal.
4. Any point on the perpendicular bisector is the same distance from either of the endpoints of the segment.
5.1 Guided Practice (p. 267)
1. If D is on the perpendicular bisector of then D isequidistant from A and B.
2. Point G must be on the bisector of by Theorem 5.4.
3.
4. and are both right angles and are congruent.
5. because C is on the perpendicular bisector of
6.
7. The distance from M to is equal to the distance fromM to
5.1 Practice and Applications (pp. 268–271)
8. No; C is not on the perpendicular bisector of becauseAC and BC are not equal.
AB
→PN.
→PL
m�LPM � m�NPM
AB.AC � BC
�BDC�ADC
AD � BD
�HJK
K
J
H
G
AB,
BMA
CD
EF
G
m�CAB � 90�
2. Sample answer:
P
4. Sample answer:
MA � MB � 32 mm
6. Sample answer:
CA � CB � 37 mm
Point D Point E Point F Point G
GB � 67 mmFB � 58 mmEB � 48 mmDB � 43 mm
GA � 67 mmFA � 58 mmEA � 48 mmDA � 43 mm
MCRBG-0501-SK.qxd 6-14-2001 11:37 AM Page 80
Geometry 81Chapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
Chapter 5 continued
9. No; the diagram does not show that
10. No; along with the information given, we would alsoneed
11. No; since P is not equidistant from the sides of P isnot on the bisector of
12. No; since we do not know for sure that one of the dis-tances given is a perpendicular distance.
13. No; the diagram does not show that the segments withequal length are perpendicular segments.
14.
16. 17.
18. Point U must be on SVvxxy, the perpendicular bisector of RT___
.
19.
20. Point M must be on JNwy, the bisector of �HJK. 21. B
22.
A
23.
m�VWU � 40�
m�VWU � m�VWX � 40�
C
24. F 25. D 26. E
27. Given: P is on m.
Prove:
Statements Reasons
1. P is on line m. 1. Given
2. 2. By construction
3. 3. Reflexive Property of Congruence
4. 4. SSS Congruence Postulate
5. 5. Corresponding parts of congruenttriangles are congruent.
6. 6. Theorem 3.1↔CP � AB
�CPA � �CPB
�CPA � �CPB
CP � CP
CA � CB
PA � PB
↔CP�AB.
m�VWU � 50� � 90�
m�VWU � m�UVW � 90�
m�XTV � 60�
m�XTV � 30� � 90�
m�XTV � m�TVX � 90�
NQ � 2
SR � 17VT � 8
AD � BD � 5 cm
A B
D
4 cm 4 cm
3 cm
�A.�A,
AP � PB.
CA � CB. 28.
Statements Reasons
1. , 1. Given
.
2. 2. Definition of segment bisector
3. and 3. Definition of perpendicular are right angles. lines
4. 4. Reflexive Property ofCongruence
5. 5. SAS Congruence Postulate
6. 6. Corresponding parts of congru-ent triangles are congruent.
7. 7. Definition of congruent segments
8. C is equidistant 8. Definition of equidistant from A and B.
29.
Statements Reasons
1. Construct inter- 1. Perpendicular Postulatesecting at a point P.
2. and are 2. Definition of perpendicular right angles. lines
3. and are 3. Definition of right trianglesright triangles.
4. 4. Given; Definition of con-gruence
5. 5. Reflexive Property ofCongruence
6. 6. HL Congruence Theorem
7. 7. Corresponding parts of con-gruent triangles are congru-ent.
8. is the perpendicular 8. Definition of perpendicularbisector of and C is bisectoron the perpendicular bisector of
30.
Statements Reasons
1. is the perpendicular 1. Givenbisector of
2. 2. Definition of perpendicular bisector of a segment
3. 3. Perpendicular Bisector Theorem
4. 4. Definition of congruent seg-ments
5. 5. Reflexive Property ofCongruence
6. 6. SSS Congruence Postulate�GMH � �GMK
GM � GM
GH � GK, MH � MK
GH � GK, MH � MK
GJ � HK, HJ � JK
HK.GJ
AB.
AB
↔CP
AP � BP
�CPA � �CPB
CP � CP
CA � CB, or CA � CB
�CPB�CPA
�CPB�CPA
AB
↔CP � AB
CA � CB
CA � CB
�APC � �BPC
CP � CP
�CPB�CPA
AP � BP
↔CP bisects AB
↔CP � AB
15.
D is inches from eachside of �A.
112
A
D3 in.
MCRBG-0501-SK.qxd 6-14-2001 11:37 AM Page 81
Chapter 5 continued
82 GeometryChapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
31. The post is the perpendicular bisector of the segmentbetween the ends of the wires.
32.
Statements Reasons
1. D is in the interior of 1. Given
2. D is equidistant from 2. Given
and
3. 3. Definition of equidistant
4. 4. Definition of distance froma point to a line
5. and are 5. If two lines are then theyright angles. form 4 right angles.
6. are 6. Definition of right triangleright triangles.
7. 7. Reflexive Property of Congruence
8. 8. HL Congruence Theorem
9. 9. Corresponding parts of congruent triangles are congruent.
10. bisects and 10. Definition of angle bisectorpoint D is on the bisector of
33. Line l is the perpendicular bisector of
34. should bisect to give the goalie equal distances
to travel on each side of .
35. increases as the puck gets closer to the goal. Thischange makes it more difficult for the goalie because thegoalie has a greater area to defend since the distances fromgoalie to the sides of (the shooting angle) increase.
36. Answers may vary.
Sample answer:
This demonstrates the Perpendicular Bisector Theorembecause D is on the perpendicular bisector of and D isequidistant from A and B.
AB
D2A � D2B � 48 mm
D1A � D1B � 40 mm
BA C
D1
D2
�APB
m�APB
→PG
�APB→PG
AB.
�ABC.
�ABC→BD
�ABD � �CBD
�DAB � �DCB
BD � BD
�DAB and �DCB
�,�DCB�DAB
DA � →BA, DC �
→BC
DA � DC
→BC.
→BA
�ABC.
37. a–c.
The perpendicular bisectors meet in one point.
d. The fire station at A should respond because it is closest to the house at X.
38.
because the product of their slopes is
because the product of their slopes is
39.
40. bisects because the perpendicular distances
from W to and are equal. We know these are
perpendicular distances because in problem 38 it was
shown that and
5.1 Mixed Review (p. 271)
41.
r � 6 cm
2r � 12
d � 12 cm
WT�→YZ.WS�
→YX
→YT
→YS
�XYZ→YW
� �10
� �1 � 9
� ���1�2 � ��3�2
WT � ��5 � 6�2 � �1 � 4�2
� �10
� �9 � 1
� ���3�2 � 12
WS � ��3 � 6�2 � �5 � 4�2
�3 � ��13� � �1�.
�1.WT�→YZ
� �13
��26
slope of YZ � m �0 � 28 � 2
� 3��3�1
slope of WT � m �1 � 45 � 6
��13
� 3 � �1�.
�1.WS�→YX
� 3�62
slope of →YX � m �
8 � 24 � 2
�1
�3� �
13
slope of WS � m �5 � 43 � 6
A
C
X
Closest to C
Closest to B
Closest to A
B
42.
37.68 cm
2 � 3.14 � 6
C � 2�r
MCRBG-0501-SK.qxd 6-14-2001 11:37 AM Page 82
Geometry 83Chapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
Chapter 5 continued
43.
45.
46. 47.
48.
49.
50.
52.
Lesson 5.2
Developing Concepts Activity (p. 272)
1.–4. Yes, all three bisectors intersect at the same point.
Conjecture: For any acute scalene triangle, the threeperpendicular bisectors of the three sides will intersectat the same point.
The three segments that are formed by connecting thevertices of the triangle to the point of intersection ofthe perpendicular bisectors of the sides have the samelength.
5.2 Guided Practice (p. 275)
1. If three or more points intersect at the same point, thelines are concurrent.
2. The word incenter is made up of the words in and center.The incenter is the “center” of the circle that is “in” thetriangle. The word circumcenter is made up of the partscircum and center. Circum can be short for circumference,which is the distance around the circle, and can help us toremember that the circumcenter is the “center” of thecircle that is “around” the triangle.
3. 4. MK � MJ � 5GC � GA � 7
AP � BP � CP � 38 mm
x � 8
6x � 48
10x � 48 � 4x
�10x � 22�� � 70� � 4x�
x � 59
x� � 31� � 90�
� 0�0
11m �
�8 � ��8�8 � ��3�
� �113
m �12 � 11�10 � 3
�87
��8�7
m �0 � 8
�7 � 0� 0�
05
m �5 � 59 � 4
� �45
�8
�10m �
5 � ��3��6 � 4
113.04 cm2
3.14 � 36
3.14�6�2
A � �r2 5.2 Practice and Applications (pp. 275–278)
5.
The perpendicular bisectors intersect outside the obtuse triangle.
7.
The perpendicular bisectors intersect at a point on the right triangle.
10. always 11. always 12. never 13. sometimes
14. 15.
16. by the Pythagorean Theorem.
17. Let the midpoint of be called point R. Then
by the Pythagorean Theorem.
18. The student’s conclusion is false because D is not thepoint of intersection of the angle bisectors. D is the pointof intersection of the perpendicular bisectors of the sidesof the triangle. So
19. The student’s conclusion is false because the angle bisec-tors of a triangle intersect in a point that is equidistantfrom the sides of the triangle, but MQ and MN are notnecessarily distances to the sides; M is equidistant from
and LJ.JK, LK,
DA � DC � DB.
QN � PQ � 25.
25 � PQ
625 � �PQ�2
576 � 49 � �PQ�2
�24�2 � �7�2 � �PQ�2
�PR�2 � �QR�2 � �PQ�2
PR � RM �PM2
�482
� 24.
PM
KB � CK � 3
CK � 3
�CK�2 � 9
16 � �CK�2 � 25
42 � �CK�2 � 52
�JC�2 � �CK�2 � �KJ�2
WB � WC � 20DR � SD � 9
51.
x � 34
2x � 34 � x
�2x � 6�� � 40� � x�
6.
The perpendicular bisectorsintersect at a point inside anacute triangle.
8. and 9.
Sample answer:
The segments are congruent. This confirmsTheorem 5.6.
A B
C
D
44.
� �5
�5
�1
m �10 � 5
�2 � ��1�
MCRBG-0501-SK.qxd 6-14-2001 11:37 AM Page 83
Chapter 5 continued
84 GeometryChapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
20. To find the point that is equidistant from each location,draw the triangle and construct the perpendicular bisectorof two sides. The point of intersection is the point that isequidistant from each location.
21. Point H is the point of intersection of the perpendicular bisectors. So H is equidistant fromeach location. H would bethe best location for the new home.
22.
Statements Reasons
1. ¤ the bisectors of 1. Givenand
2. 2. bisects so D isequidistant from the sidesof
3. 3. bisects so D isequidistant from the sidesof
4. 4. Transitive property ofequality
5. D is on the bisector 5. Converse of the Angle of Bisector Theorem
6. D is equidistant from 6. Givens and Steps 2, 3,and and 4
23. She could construct the perpendicular bisectors to findthe point that is equidistant from the vertices of the trian-gle. By doing so, she would see that the perpendicularbisectors do intersect at a point on the hypotenuse. Sincethe point on the hypotenuse would be the point of inter-section of the perpendicular bisectors, then it would beequidistant from the vertices.
24.–25. The radius isapproximately
26. ft inches
30 in. in. per year years
The mycelium is approximately 3.75 years old.
� 3.75� 8
� 30212
212 ft.
1
1
y
x
A (2, 5)
B (6, 3)
C (4, 1)
CA.BC,AB,
�C.
DF � DG
�ABC.
�ABC,→BDDE � DF
�BAC.
�BAC,→ADDE � DG
DG � CA
DF�BC,DE�AB,�C,�B,�A,
ABC,
School
Office
FactoryH
27.
E
28.
(Pythagorean Theorem)
because T is the midpoint of
C
29. The midpoint of is
The midpoint of is
The midpoint of is
The slope of
The perpendicular bisector has slope because
is an equation of the perpendicular bisector of
The slope of
—CONTINUED—
BC �0 � 6
18 � 12�
�66
� �1.
AB.y � �2x � 15
y � 3 � �2x � 12
y � 3 � �2�x � 6�
�2 �12
� �1.
�2
AB �6 � 0
12 � 0�
612
�12
.
�0 � 182
, 0 � 0
2 � � �182
, 02� � �9, 0�.
AC
�12 � 182
, 6 � 0
2 � � �302
, 62� � �15, 3�.
BC
�0 � 122
, 0 � 6
2 � � �122
, 62� � �6, 3�.
AB
XY � 10
XY � 2 � 5
XY.
XY � 2�XT�
XT � 5
�XT�2 � 25
�XT�2 � 144 � 169
�XT�2 � 122 � 132
�XT�2 � �TW�2 � �XW�2
XW � WZ � 13
m�ADC � 140�
m�ADC � 40� � 180�
m�ADC � m�DCA � m�CAD � 180�
m�DCA � m�CAD � 40�
12 �m�BCA� �12 �m�CAB� � 40�
12 �m�BCA � m�CAB� �12 � 80�
m�BCA � m�CAB � 80�
100� � m�BCA � m�CAB � 180�
m�ABC � m�BCA � m�CAB � 180�
MCRBG-0501-SK.qxd 6-14-2001 11:38 AM Page 84
Geometry 85Chapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
Chapter 5 continued
29. —CONTINUED—
The perpendicular bisector of has slope 1 because
is an equation of the perpendicular bisectorof
The slope of so is
horizontal.
So the perpendicular bisector is the vertical line
30. The lines and intersect at the pointbecause
To show is also on substitute x � 9and y � �3 in the equation.
Since is true, the point is on the line
31. Let P be the point
Since P is equidistant from A,B, and C.
AP � BP � CP � 3�10,
� 3�10
� �9 � �10
� �90
� �81 � 9
� ���9�2 � ��3�2
CP � ��9 � 18�2 � ��3 � 0�2
� 3�10
� �9 � �10
� �90
� �9 � 81
� ���3�2 � ��9�2
BP � ��9 � 12�2 � ��3 � 6�2
� 3�10
� �9 � �10
� �90
� �81 � 9
� �92 � ��3�2
AP � ��9 � 0�2 � ��3 � 0�2
�9, �3�.
y � x � 12.�9, �3��3 � �3
�3 � �3
�3 � 9 � 12
y � x � 12
y � x � 12,�9, �3�y � �2�9� � 15 � �18 � 15 � �3.�9, �3�
x � 9y � �2x � 15
x � 9.
ACAC �0 � 0
18 � 0�
018
� 0,
BC.y � x � 12
y � 3 � x � 15
y � 3 � 1 � �x � 15�
�1 � 1 � �1.BC
5.2 Mixed Review (p. 278)
32.
34. j has slope because
An equation of j is
35. j has slope because
An equation of is
36. j has slope because
An equation of j is
37. j has slope because
An equation of j is
38. There is enough information to prove byusing the SAS Congruence Postulate.
39. There is not enough information given to proveOne pair of congruent sides, one side
congruent to itself, and one pair of congruent angles aregiven. But the angles must be the included angles and theyare not.
40. There is enough information given to proveOne pair of congruent legs and one
pair of congruent hypotenuses are given. The HLCongruence Theorem can be used to prove
Lesson 5.3
5.3 Guided Practice (p. 282)
1. The centroid of a triangle is the point where the threemedians intersect.
2. The legs, and of right are also altitudesof because is the perpendicular segment fromK to and is the perpendicular segment from L toKM.
LMLMKM�KLM
�KLMLM,KM
�PMN � �KML.
�PMN � �KML.
�GJF � �GJH.
�ABC � �DEC
y � �1110 x �
565 .
y � �1110 x �
565
y � 9 � �1110 x �
115
y � 9 � �1110 �x � 2�
y � ��9� � �1110 �x � ��2��
�1110 � 10
11 � �1.�1110
y �32 x � 5.
y �32 x � 5
y � 8 �32 x � 3
y � 8 �32 �x � 2�
�23 � 3
2 � �1.32
y �12 x �
52.j
y �12 x �
52
y � 6 �12 x �
72
y � 6 �12 �x � 7�
�2 � 12 � �1.1
2
y � �13 x �
133 .
y � �13 x �
133
y � 4 � �13 x �
13
y � 4 � �13 �x � 1�
�13 � 3 � �1.�
13
� 22.5 square units
� 452
� 12 � 9 � 5
A �12 bh 33.
� 77 square units
� 1542
� 12 � 22 � 7
A �12 bh
MCRBG-0502-SK.qxd 5-25-2001 11:08 AM Page 85
Chapter 5 continued
86 GeometryChapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
3. indicates that G is the midpoint of Therefore, is a median of
4. indicates that is an altitude of
5. indicates the is bisected. So is an angle bisector of
6. and indicates G is the midpoint ofand is a perpendicular bisector of but it is
also a median, an altitude, and an angle bisector sinceby the SAS Congruence Postulate so
7. indicates and In this case is a
perpendicular bisector, an angle bisector, a median, andan altitude of
5.3 Practice and Applications (pp. 282–284)
8.
9. 10.
11.
12.
13.–14. Sample answer:
is an acute triangle.
15. Yes, they all met at the same point. It is labeled as pointD.
�ABC
A
LD
N
M B
C
PHEP
�48
�12
PHEH
�4
12�
13
� 48 units
� 15 � 15 � 18
� 2 � 7.5 � 15 � 2 � 9
� 2�DG� � 15 � 2�DH�
Perimeter of �DEF � DE � EF � FD
15 � EF
225 � �EF�2
144 � 81 � �EF�2
122 � 92 � �EF�2
�EH�2 � �HF�2 � �EF�2
12 � EH
PH � 4 32 � 8 � EH
PH � 8 � 12 8 �23 EH
PH � PE � EH EP �23 EH
FH � DH � 9
�DEF.
EGDG � FG.�DGE � �FGE,�DEG � �FEG,�DGE � �FGE
�DEG � �FEG.�DGE � �FGE
�DEF,EGDFDG � FGEG�DF
�DEF.EG�DEF�DEG � �FEG
�DEF.EGEG�DF
�DEF.EGDF.DG � FG 16. Sample answer:
The distance from the centroid to a vertex is two thirds ofthe distance from that vertex to the midpoint of the oppo-site side.
17.
18.
19.
The coordinates of T are
20.
21. � �4, 4�� �82
, 82�M � �5 � 3
2,
2 � 62 �
NTNR
�69
�23
NR � 11 � 2 � 9
NT � 11 � 5 � 6
� �2, 2�� �42
, 42� R � ��1 � 5
2,
�2 � 62 �
�5, 6 � 4� � �5, 2�.
PT � 4
PT �23 � 6
PT �23 PQ
� 6
� �36
� �0 � 36
� �02 � ��6�2
PQ � ��5 � 5�2 � �0 � 6�2
� �5, 0�� �102
, 02�Q � ��1 � 11
2,
�2 � 22 �
40 � 40
40 �23 � 60
CD �23 �CM�
CM � 60 mm
CD � 40 mm
54 � 54
54 �23 � 81
BD �23 �BL�
BL � 81 mm
BD � 54 mm
64 � 64
64 �23 � 96
AD �23 �AN�
AN � 96
AD � 64 mm
MCRBG-0502-SK.qxd 5-25-2001 11:08 AM Page 86
Geometry 87Chapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
Chapter 5 continued
22.
23.
24. Sample answer:
P is the orthocenter of
25. Sample answer:
The orthocenter of ispoint G.
26. Sample answer:
P is the orthocenter of
27.C
FA B
D
GH
E
�KLM.
P
K
ML
�EFGE
G F
�ABC.
A
P
B
C
2�5 � 2�5
2�5 �23 � 3�5
JP �23 JM
� 3�5
� �9 � �5
� �45
� �9 � 36
� ���3�2 � ��6�2
JM � ��4 � 7�2 � �4 � 10�
� 2�5
� �4 � �5
� �20
� �4 � 16
� ���2�2 � ��4�2
JP � ��5 � 7�2 � �6 � 10�2 28. G and H are the same point.
29. When is measured, it is found that Sincethen G and H must be the same point; therefore
the lines containing the three altitudes intersect at onepoint.
30.–32.
33. The measure of the angle between r and is approxi-mately
34. a.
b.
c. Check drawings.
d.
The length of the altitude is equal to twice the area divid-ed by the base.
12 � BE
90 � 7.5 � BE
90 �12
� 15 � BE
90 �12
� CA � BE
A �12
bh
� 90 square units�12
� 20 � 9A �12
bh
CD � 9
�CD�2 � 81
144 � �CD�2 � 225
122 � �CD�2 � 152
�AD�2 � �CD�2 � �AC�2
20�.MP
R
Sr
B
L
D
C
M
P
GH � 0,GH � 0.GH
e.
2Ab
� h
2A � bh
A �12
bh
MCRBG-0502-SK.qxd 5-25-2001 11:08 AM Page 87
Chapter 5 continued
88 GeometryChapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
35.
Statements Reasons
1. is isosceles; 1. Givenis a median to base
2. D is the midpoint of 2. Definition of median
3. 3. Definition of midpoint
4. 4. Definition of isosceles triangle
5. 5. Reflexive Property ofCongruence
6. 6. SSS Congruence Postulate
7. 7. Corresponding parts ofcongruent triangles arecongruent.
8. and are a 8. Definition of linear pairlinear pair.
9. 9. If two lines intersect toform a linear pair of con-gruent angles, then thelines are perpendicular.
10. is also an altitude. 10. Definition of altitude
36. No, medians to the legs of an isosceles triangle are notperpendicular to the legs (unless the triangle is actuallyequilateral).
37. Yes, the medians of an equilateral triangle are also alti-tudes because the proof for the isosceles triangle could beused for the equilateral triangle.
Yes, the medians would be contained in the angle bisec-tors. By looking at the proof in Exercise 35, it can beseen that the median was also the angle bisector since thetwo triangles are congruent.
Yes the medians would be contained in the perpendicularbisectors because it was shown in Exercise 35 that themedian was perpendicular to the side at the midpoint.
38. The median of an equilateral triangle is also a perpendic-ular bisector of a side, an altitude, and an angle bisector.
5.3 Mixed Review (p. 284)
39. The parallel line would also have slope
An equation of the line through P that is parallel tois y � �x � 8.y � �x � 3
y � �x � 8
y � 7 � �x � 1
y � 7 � �1�x � 1�
�1.
BD
BD�AC
�BDA�BDC
�BDC � �BDA
�BDC � �BDA
BD � BD
AB � CB
AD � CD
AC.
AC.BD�ABC
40. The parallel line would also have slope
An equation of the line through P that is parallel tois
41. The parallel line would also have slope 3.
An equation of the line through P that is parallel tois
42. The parallel line would also have slope
An equation of the line through P that is parallel tois
43. because you need the angles which do nothave or as a side.
44. because you need the angles which have oras a side.
45. Sample answer:
Quiz 1 (p. 285)
1.
x � 16
4x � 3x � 16
4x � 9 � 3x � 25
� 5�10
� �25 � �10
� �250
� �169 � 81
� �132 � 92
h � ��13 � 0�2 � �0 � 9�2
1
1
y
x
(0, 9)
(13, 0)
HJEF�F � �J
GJDF�E � �H
y � �12 x.y � �
12 x � 1
y � �12 x
y � 2 � �12 x � 2
y � ��2� � �12 �x � 4�
�12.
y � 3x � 21.y � 3x � 5
y � 3x � 21
y � 9 � 3x � 12
y � ��9� � 3�x � 4�
y � �2x � 14.y � �2x � 3
y � �2x � 14
y � 8 � �2x � 6
y � 8 � �2�x � 3�
y � ��8� � �2�x � ��3��
�2.
2.
y � 12
2y � 24
3y � y � 24
MCRBG-0502-SK.qxd 5-25-2001 11:08 AM Page 88
Geometry 89Chapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
Chapter 5 continued
3.
4. because the perpendicular bisectors intersect at a point equidistant from the vertices of the triangle.
5. The balancing point would be at point G because that isthe centroid of the triangle.
5.3 Math and History (p. 285)
1. You need to go to the post office (P), then the market(M), then the library (L) or in reverse order.
2. The goalie’s position on the angle bisector optimizes thechance of blocking a scoring shot because the distancethe goalie would have to travel to protect either side ofthe goal would be the same.
Technology Activity 5.3 (p. 286)
Investigate
1. �
So is the angle bisector of
2. F was the point of intersection of the angle bisectors of angles and by construction. Since
AFxxxy is the angle bisector of Because angle bisector AFxxxy passes through the
intersection point, F, of BDxxxxy and CExxxy, the three anglebisectors are concurrent.
3. This makes a median also.
4. F was the point of intersection of two medians by con-struction. Since G is the midpoint of and
is the third median of the triangle. Since F is on by construction, F is on all three medians and the medi-ans are concurrent.
5. Sample measures are given:
Yes,
6. No, the quotient does not change.
Extension
For any triangle in which the angle bisector is containedin the same line as the median, the line will also containan altitude and perpendicular bisector of the triangle.
—CONTINUED—
ADAF
AD �23 AF
ADAF
�72
108�
23
AF � 108 mm
AD � 72 mm
CGCGABAG � BG,
CGAG � BG.
�BAC.m�BAF � m�CAF,
�BCA�ABC
�BAC.→AF
m�CAFm�BAF
VT � VS � 10
10 � VT
100 � �VT�2
36 � 64 � �VT�2
62 � 82 � �VT�2 This will occur for the bisector of the vertex angle of anisosceles triangle and for the bisector of each angle of anequilateral triangle.
Given: ADxxxxy bisects �BAC andADxxxx is a median.
Prove: ADxxxx is an altitude andADxxxx is a perpendicularbisector of BCxxxx.
In this drawing is the angle bisector of andis the median of the triangle. So Sinceis the angle bisector, or
Then by the HL Congruence Theorem.Therefore, or because corresponding parts of congruent triangles arecongruent. Also by the HL CongruenceTheorem. So, or because corresponding parts of congruent triangles arecongruent. Then
So which are linear pairs.Therefore, and This wouldmean that would be an altitude and a perpendicularbisector, also.
Lesson 5.4
5.4 Guided Practice (p. 290)
1. In if M is the midpoint of N is the midpointof and P is the midpoint of then and
are midsegments of triangle
2. It is convenient to position one of the sides of the trianglealong the x-axis because some of the coordinates of twoof the points will be zero and one side will be horizontaland have a slope of 0.
3. 4.
5.
7.
9.
� 30.6
� 10.6 � 8 � 12
Perimeter � GJ � JH � GH
� 10.6
� 12 � 21.2
GJ �12 � EF
� 16
� 2 � 8
DF � 2 � DG
� 21.2
� 2 � 10.6
EF � 2 � EH
GH � DEJH � DF
�ABC.PNNP,MN,BC,AC,
AB,�ABC,
ADAD�CD.�ADC � �ADB
m�ADC � m�ADBm�ADE.m�CDF � m�ADF � m�BDE �
m�CDF � m�BDE�CDF � �BDE�CFD � �BED
m�ADE � m�ADF�ADE � �ADF�ADE � �ADF
AD � AD.DE � DF.DE � DF
→AD
DC � DB.AD�BAC
→AD
A E B
D
CF
6.
8.
� 8
� 12 � 16
JH �12 � DF
� 12
� 12 � 24
GH �12 � DE
MCRBG-0503-SK.qxd 5-25-2001 11:08 AM Page 89
Chapter 5 continued
90 GeometryChapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
10.
11.
12. 13.
14.
15.
16.
17.
19. and are congruent by theCorresponding Angles Postulate, as are and
and bythe Alternate Interior Angles Theorem.
So, by the Transitive Property of Congruence,and are congruent, as are and Then
and all congruent by the Third AnglesTheorem and the Transitive Property of Congruence.
20. Sample answer:
Use the construction of the perpendicular bisectors of thesides to find the midpoints D, E, and F.
are the midsegments of �ABC.DE, EF, and DF
A B
E
C
F
D
�MNC are�B, �ALM, �LMN,�NLM.�LMA,�C,
�BNL,�LNM�A, �NMC,�BLN,
�NMC � �LNM�LMA � �NLM�LMA.�BNL, �C,
�NMC�BLN, �A,
� 31
� 24 � 7
� 3 � 8 � 7
LM � 3x � 7
x � 8
�12 x � �4
3x �72 x � 4
3x � 7 �72 x � 3
3x � 7 �12 �7x � 6�
LM �12 � BC
� 18
� 2 � 9
BC � 2 � NC
� 14� 2 � 7AB � 2 � MN
� 10�12 � 20LN �
12 � AC
AB � MNLM � BC
AB � 5.4 � 10 yd � 54 yd
� �29 � 5.4
� �25 � 4
� �52 � 22
AB � ��6 � 1�2 � �6 � 4�2
� �1, 4�
� 22
, 82
A � 0 � 22
, 0 � 8
2 21.
22. Slope of
Slope of
Since the slopes of and are equal,
So and
23.
24.
—CONTINUED—
�b
a � c
�2b
2�a � c�
�2b
2a � 2c
Slope of CB �2b � 02a � 2c
�b
a � c
Slope of DF �b � 0a � c
� �c, 0�� 2c2
, 02F � 0 � 2c
2,
0 � 02
y
xA(0, 0) F (c, 0) B(2c, 0)
E(a � c, b)
C (2a, 2b)
D (a, b)
DF �12
BC.BC � DF
DF �12
BC
�12
� �89��89
2�
�89�4
��894
DF � �22.25
� �89
� �25 � 64
� �52 � 82
BC � ��10 � 5�2 � �6 � ��2��2
� �22.25
� �6.25 � 16
� �2.52 � 42
DF ��5 �52
2
� �4 � 0�2
BC � DF.DFBC
�85
� 4 �25
�452
DF �4 � 0
5 �52
�85
BC �6 � ��2�
10 � 5
� �5, 4�� 102
, 82F � 0 � 10
2,
2 � 62
� 152
, 2� 152
, 42E � 5 � 10
2,
�2 � 62
� 52
, 0� 52
, 02D � 0 � 5
2,
2 � ��2�2
� �6, 6�
� 122
, 122
B � 2 � 102
, 8 � 4
2
18.
� 6
� 24 � 18
� 6 � 4 � 18
AB � 6x � 18
x � 4
�2x � �8
x � 3x � 8
x � 1 � 3x � 9
x � 1 �12 �6x � 18�
MN �12 � AB
� 9
� NC
LM �12 � BC
MCRBG-0503-SK.qxd 5-25-2001 11:08 AM Page 90
Geometry 91Chapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
Chapter 5 continued
24. —CONTINUED—
Since the slopes of and are equal,
Since the slopes of and are equal,
25.
26.
Slope of
Draw a line through M with slope
Slope of
Draw a line through L with slope 5.
MN �9 � 45 � 4
�51
� 5
13
.
LN �4 � 34 � 1
�13
2
2
y
x
M(5, 9)
N(4, 4)L(1, 3)
C B
A
�12 CA
�12 � 2�a2 � b2
EF � �a2 � b2
�12 CB
�12 �2��a � c�2 � b2�
DF � ��a � c�2 � b2
� 2�a2 � b2
� �4�a2 � b2
� �4�a2 � b2�
� �4a2 � 4b2
� ��2a�2 � �2b�2
CA � ��2a � 0�2 � �2b � 0�2
� 2��a � c�2 � b2
� �4��a � c�2 � b2
� �4��a � c�2 � b2�
� �4�a � c�2 � 4b2
� �22�a � c�2 � �2b�2
CB � ��2a � 2c�2 � �2b � 0�2
� �a2 � b2
EF � ��a � c � c�2 � �b � 0�2
� ��a � c�2 � b2
DF � ��a � c�2 � �b � 0�2
EF � CA.CAEF
�ba
�2b2a
Slope of CA �2b � 02a � 0
�ba
Slope of EF �b � 0
a � c � c
DF � CB.CBDF
Draw a line through N with slope
The lines intersect at and
27.
Draw a line through M with slope
Draw a line through L with slope
Draw a line through N with slope
The lines intersect at and
28.
because
29.
� 31 units� 12 � 10 � 9P � SU � TU � ST
� 9
� QU
ST �12�QR�
� 10
� 12�20�
TU �12 PQ
� 40 units� 14 � 16 � 10P � CD � BD � BC
� 10
� 2 � 5
� 2�GC�
BG � GC. � GC � GC
BC � BG � GC
16 � BD
8 �12 BD
GF �12 BD
C�7, 9�.B�11, 3�,A�3, �1�,
52
.
Slope of LM �6 � 19 � 7
�52
12
.
�24
�12
Slope of MN �6 � 49 � 5
�32
.
�3
�2� �
32
Slope of LN �4 � 15 � 7
�2
2
y
x
M(9, 6)
L(7, 1)
N(5, 4)
A
C
B
C�2, 8�.A�0, �2�, B�8, 10�,
32
.
Slope of LM �9 � 35 � 1
�64
�32
MCRBG-0503-SK.qxd 5-25-2001 11:08 AM Page 91
Chapter 5 continued
92 GeometryChapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
30.
Perimeter of is 4 times the perimeter of
31. The perimeter of the shaded triangle in Stage 1 is because the length of each side of the shaded triangle is the length of a side in the original triangle.
The total perimeter of the shaded triangle in Stage 2 is
The total perimeter of the shaded triangles in Stage 3 is
32. The bottoms of the legs will be 60 inches apart. Since thecross bar attaches at the midpoints of the legs, the crossbar is a midsegment of the triangle formed by the twolegs and the ground. Since the length of the midsegmentis half of the length of third side, the length of the crossbar, 30 inches, is half of the distance between the bottomsof the legs, 60 inches.
33. is a midsegment of so D is the midpoint ofand By the Midsegment Theorem,
and But F is the midpoint of soThen by the transitive property of equality
and the definition of congruent segments,Corresponding angles and are congruent,so by the SAS Congruence Postulate.�ADE � �DBF
�ABC�ADEDE � BF.
BF �12 BC.
BC,DE �12 BC.DE � BC
AD � DB.AB�ABC,DE
� 238.
12 �
14 �
14 �
14 �
18 �
18 �
18 �
18 �
18 �
18 �
18 �
18 �
18
12 �
14 �
14 �
14 � 11
4.
12
12
Perimeter of �GHI �14 of perimeter of �ABC
� 14 �BC � AC � AB�
� 14 BC �
14 AC �
14 AB
Perimeter of �GHI � GH � HI � GI
� 14 AB
� 12 �1
2 AB� GI �
12 FE
� 14 AC
� 12 �1
2 AC� HI �
12 DE
� 14 BC
� 12 �1
2 BC� GH �
12 FD
�GHI.�ABC
A B
E
C
F H
I G
D
34. In Exercise 33, it was shown that andSo all that is left to show is that
This can be done in the same manner that it was shownthat By using the fact that is a midsegmentof �ABC, By using the fact that E is themidpoint of we can get Therefore,
or and the triangles are congruent bythe SSS Congruence Postulate.
35. Since is closer to than it must be longer thanSince is the midsegment, or
So cannot be 10 or 12 feetlong since it must be longer than , which is 12 feetlong. could be 14 feet long but not 24 feet long sincePQ cannot equal RS. So, or
36. a.
b.
c. The line containing has slope �2 and passesthrough F(4, 5).
An equation of CBvxxy is y � 5 � �2(x � 4).
d.
The line containing has slope 3 and passes through
An equation of is
The line containing has slope and passes through
An equation of is
e. :
—CONTINUED—
y �12 x �
12
y � 2 �12 x �
32
y � 2 �12 �x � 3�
↔AB :
y � 3x � 2 y � �2x � 13
y � 4 � 3x � 6y � 5 � �2x � 8
y � 4 � 3�x � 2�↔ACy � 5 � �2�x � 4�
↔BC :
y � 2 �12 �x � 3�.
↔AB
y � 2 �12 �x � 3�
E�3, 2�.
12AB
y � 4 � 3�x � 2�.↔AC
y � 4 � 3�x � 2�
D�2, 4�.AC
�12
slope of FD � m3 �5 � 44 � 2
� 3�31
slope of EF � m2 �5 � 24 � 3
y � 5 � �2�x � 4�
CB
� �2�2
�1slope of DE � m1 �
4 � 22 � 3
1
1
y
x
F (4, 5)
E(3, 2)A(1, 1)
C (3, 7)
B(5, 3)(2, 4)
D
12 < PQ < 24.MN < PQ < RS,
PQMN
PQMN �12 � 24 � 12 feet.
MN �12 RSMNMN.
MN,RSPQ
AE � DFAE � DFAE �
12 AC.AC,
DF �12 AC.
DEDE � BF.
AE � DF.DE � BF.AD � DB
MCRBG-0503-SK.qxd 5-25-2001 11:08 AM Page 92
Geometry 93Chapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
Chapter 5 continued
f. To find A, find the point of intersection of and
has the equation
has the equation
By substitution,
So,
To find B, find the point of intersection of and
has the equation
has the equation
By substitution,
So,
To find C, find the point of intersection of and
has the equation
has the equation
By substitution,
So,
37.
C�3, 7�.
y � 9 � 2 � 7
y � 3 � 3 � 2
y � 3x � 2
x � 3
5x � 15
3x � �2x � 15
3x � 2 � �2x � 13
y � �2x � 13.↔BC
y � 3x � 2.↔AC
↔BC.
↔AC
B�5, 3�.
y � 3
y � �10 � 13
y � �2 � 5 � 13
y � �2x � 13
x � 5
52 x �252
12 x � �2x �255
12 x �
12 � �2x � 13
y � �2x � 13.↔BC
y �12 x �
12.
↔AB
↔BC.
↔AB
A�1, 1�.
y � 3 � 2 � 1
y � 3 � 1 � 2
y � 3x � 2
x � 1
�52 x � �
52
12 x � 3x �52
12 x �
12 � 3x � 2
y � 3x � 2.↔AC
y �12 x �
12.
↔AB
↔AC.
↔AB 38. is the function
that gives the length of themidsection at Stage n. Fromone stage to the next, thelength is multiplied by
5.4 Mixed Review (p. 293)
39.
Addition property of equality
40.
Subtraction property of equality
Division property of equality
41.
Addition property of equality
Subtraction property of equality
Division property of equality
42.
Subtraction property of equality
Subtraction property of equality
Division property of equality
43.
Division property of equality
Addition property of equality
Division property of equality
44.
Division property of equality
Subtraction property of equality
Division property of equality
45.
Subtraction property of equality
Division property of equality
Subtraction property of equality
46.
Distributive property
Simplify
Subtraction property of equality
Division property of equality x � 6
5x � 30
5x � 10 � 40
3x � 2x � 10 � 40
3x � 2�x � 5� � 40
x � �11
x � 1 � �10
�2�x � 1� � 20
�2�x � 1� � 3 � 23
x � �73
3x � �7
3x � 10 � 3
9�3x � 10� � 27
x � 2
4x � 8
4x � 1 � 7
2�4x � 1� � 14
x � 4
�4x � �16
5x � 9x � 16
5x � 12 � 9x � 4
x � 3
6x � 18
8x � 2x � 18
8x � 1 � 2x � 17
x � 11
3x � 33
3x � 13 � 46
x � 14
x � 3 � 11
12.
y � 24 � �12�n
Stage
8
4
0
12
16
20
24
2 4 61 3 5
Mid
seg
men
t
len
gth
y
n
Stage n 0 1 2 3 4 5
Midsegment length 24 12 6 3 1.5 0.75
MCRBG-0504-SK.qxd 5-25-2001 11:08 AM Page 93
Chapter 5 continued
47.
48.
49.
50. and because and are angle bisectors and angle bisectors divide anangle into two congruent angles.
51. Point D is the incenter of because it is the inter-section of the angle bisectors of
52. because D is the point of intersection ofthe angle bisectors of and D is equidistant fromthe sides of the triangle.
53.
But because D is equidistant from the sides of
So,
Lesson 5.5
Technology Activity 5.5 (p. 294)
Investigate
1. The longest side is opposite the largest angle.
2. The shortest side is opposite the smallest angle.
3. The answers are the same.
The longest side is opposite the largest angle.
The shortest side is opposite the smallest angle.
4. The longest side will always be opposite the largestangle. The shortest side will always be opposite thesmallest angle. The side with the middle length will beopposite the angle with the middle measure.
DF � DE � 6.
�ABC.DE � DF
DE � 6
�DE�2 � 36
�DE�2 � 64 � 100
�DE�2 � 82 � 102
�DE�2 � �EC�2 � �CD�2
�ABCDE � DG � DF
�ABC.�ABC
→CD
→BD,
→AD,�BCD � �ACD�CAD � �BAD
x � 18
�3x � �54
4x � 7x � 54
4x� � 61� � �7x � 7��
x � 7
17x � 119
17x � 61 � 180
�10x � 22�� � �7x � 1�� � 38� � 180�
x � 23
2x � 46
2x � 134 � 180
�x � 2�� � 132� � x� � 180� Extension
Sample answer:
The statement is false because the above example is acounterexample.
5.5 Guided Practice (p. 298)
1. The 1 inch side is opposite the smallest angle of theinch side is opposite the middle angle of and the
inch side is opposite the largest angle of
2. No, it is not possible to draw a triangle with side lengthsof 5 inches, 2 inches, and 8 inches because the sum of the lengths of any two sides of a triangle must be greaterthan the length of the third side. But is not greaterthan 8.
3.
The smallest angle is and the largest angle is
4. The shortest side is and the longest side is
5. The distance between Guiuan and Masbate has to begreater than miles and less than
miles.
5.5 Practice and Applications (pp. 298–301)
6.
is the shortest side because it is opposite the smallestangle.
is the longest side because it is opposite the largestangle.
7.
is the shortest side. and are the longest sides
8.
is the shortest side. is the longest side.HJJK
m�J � 55�
m�J � 35� � 90�
m�J � m�H � 90�
�RS � ST�.STRSRT
m�R � 65�
m�R � 115� � 180�
m�R � 50� � 65� � 180�
m�R � m�S � m�T � 180�
AB
AC
m�A � 67�
m�A � 113� � 180�
m�A � 42� � 71� � 180�
m�A � m�B � m�C � 180�
165 � 99 � 264165 � 99 � 66
DE.EF
�F.�D
m�E � 45�
m�E � 135� � 180�
32� � m�E � 103� � 180�
m�D � m�E � m�F � 180�
5 � 2
90�.218
62�,178
28�,
length of shortest sidelength of longest side
�63 mm96 mm
� 0.656
measure of smallest anglemeasure of largest angle
�41�
82�� 0.5
94 GeometryChapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
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Geometry 95Chapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
Chapter 5 continued
9. is the smallest angle. is the largest angle.
10. is the smallest angle. is the largest angle.
11. is the smallest angle. is the largest angle.
12. 13.
14. and
15.
and
16.
and
17. and 18. and
19. and
20.–23. Answers may vary; sample answers are given.
20.
21. 22.
23. The following combinations of lengths will not producetriangles: 4 inches, 4 inches, and 10 inches; 3 inches, 5inches, and 10 inches; and, 2 inches, 7 inches, and 9inches.
24.
x < 7
�x > �7
2x > 3x � 7
2x � 5 > 3x � 2
x � 2 � x � 3 > 3x � 2
AB � AC > BC
5.5 in.
8.5 in.4 in.
7 in.
6 in.5 in.
2 in.4 in.
8 in. 6 in.
5 in.
8 in.7 in. 7 in. 8 in.
6 in. 6 in.5 in.
�R�T, �S,
�P�N, �Q,�M�L, �K,
HGHJ, JG,
m�G � 25�
m�G � 155� � 180�
m�HGJ � 120� � 35� � 180�
m�G � m�J � m�H � 180�
EFDF, DE,
m�F � 60�
120� � m�F � 180�
90� � 30� � m�F � 180�
m�D � m�E � m�F � 180�
ACAB, BC,
x� > z�
x� > y�y� � z� � x�
�F�H
�Q�R
�B�C 25.
26. It is shorter to cut across the empty lot because the sumof the lengths of the two sidewalks is greater than thelength of the diagonal across the lot. If the corner ofPleasant Street and Pine Street were labeled point A, thecorner of Pine Street and Union Street were labeled pointB, and the corner of Union Street and Oak Hill Avenuewere labeled point C, could be formed. By theTriangle Inequality Theorem, that is,walking around the sidewalks is longer than walkingthrough the lot.
27. The sides and angles could not be positioned as they arelabeled; for example, the longest side is not opposite thelargest angle.
28. No, a kitchen triangle cannot have side lengths of 9 feet,3 feet, and 5 feet because 3 � 5 � 8 and 8 is not greaterthan 9.
29. The boom is raised when the boom lines are shortened.
30. AB must be less than feet.
31. Yes, when the boom is lowered and length of the boomlines, AB, is greater than 100 feet, then will belarger than
32. The third inequality would be and this isnot helpful because since x is positive, x � 14 > 10 forall values of x.
33. so is a right triangle. The largest anglein a right triangle is the right angle, so
so (If one angle of atriangle is larger than another then the side oppositethe larger angle is longer than the side opposite the smaller angle.)
�,MN > MJ.m�MJN > m�MNJ,
�MJNMJ�JN,
x � 14 > 10
�BAC.�ABC
100 � 50 � 150
AB � BC > AC;�ABC
x < 7
�x > �7
2x > 3x � 7
2x � 6 > 3x � 1
x � 2 � x � 4 > 3x � 1
AB � AC > BC
MCRBG-0504-SK.qxd 5-25-2001 11:08 AM Page 95
Chapter 5 continued
34.
Statements Reasons
1. 1. Given
2. Extend to D such 2. Ruler Postulatethat
3. 3. Segment Addition Postulate
4. 4. Base Angles Theorem
5. 5. Protractor Postulate
6. 6. Substitution property of equality
7. 7. If one angle of a triangle islarger than another angle, thenthe side opposite the largerangle is longer than the sideopposite the smaller angle.
8. 8. Substitution property of equality
9. 9. Substitution property of equality
35. since the side opposite the angle of is longerthan the side opposite the angle of A
36. is the measure of the exterior angle and B
37. D
38.
Statements Reasons
1. 1. Given
2. Let D be a point on 2. A plane contains at least plane M distinct from C. three noncollinear points.
3. 3. Definition of a line perpendicular to a plane
4. is a right angle. 4. If two lines are perpendic-ular, then they intersect toform four right angles.
5. is a right triangle. 5. Definition of right triangle
6. is an acute angle. 6. The non-right angles in aright triangle are acuteangles.
7. 7. Definition of an acuteangle
8. 8. Definition of a right angle
9. m�PDC < m�PCD 9. Substitution property ofequality
10. 10. If one angle of a triangle islarger than another angle,then the side opposite thelarger angle is longer thanthe side opposite thesmaller angle.
PD > PC
m�PCD � 90�
m�PDC < 90�
�PDC
�PCD
�PCD
↔CD�PC
PC�plane M
x� � y� � z�.z�
y� �n � 3 > n�.x�x� > y�
AB � AC > BC
AD � AC > BC
DC > BC
m�DBC > m�1
m�DBC > m�2
�1 � �2
AD � AC � DC
AB � AD.AC
�ABC
5.5 Mixed Review (p. 301)
39.–41. Answers may vary. Sample answers are given.
39. The proof for Example 2 on page 230 is a two-columnproof.
40. The proof for Example 1 on page 229 is a paragraphproof.
41. The proof for Example 3 on page 158 is a flow proof.
42. and are corresponding angles. So are and
43. and are vertical angles.
44. and are alternate interior angles. So are and
45. and are alternate exterior angles. So are and
46.
The line containing has slope and passes through
The line containing has slope and passes through
The line containing has slope and passes through
—CONTINUED—
y �12
x �52
y � 1 �12
x �32
y � ��1� �12
�x � 3�
N�3, �1�.
12
,BC
y � �25
x �195
y � 3 � �25
x �45
y � 3 � �25
�x � 2�
M�2, 3�.
�25
AC
y � �4x � 7
y � 1 � �4x � 8
y � 1 � �4�x � 2�
y � 1 � �4�x � ��2��
L ��2, 1�.�4AB
� �25
�2
�5slope of LN � m3 �
1 � ��1��2 � 3
� �4�4
�1slope of MN � m2 �
3 � ��1�2 � 3
�12
�24
slope of LM � m1 �3 � 1
2 � ��2�
�10.�7�2�7
�11.�6�3�6
�9�12
�9.�5�1�5
96 GeometryChapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
MCRBG-0504-SK.qxd 5-25-2001 11:08 AM Page 96
Geometry 97Chapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
Chapter 5 continued
46. —CONTINUED—
To find A, find the point of intersection of and
The point A has coordinates
To find B, find the point of intersection of and
The coordinates of B are
To find C, find the point of intersection of and ↔BC.
↔AC
��1, �3�.
y � �3
y � 4 � 7
y � �4��1� � 7
y � �4x � 7
x � �1
�92
x �92
�4x �12
x �92
�4x � 7 �12
x �52
y �12
x �52
y � �4x � 7
↔BC.
↔AB
��3, 5�.
y � 5
y � 12 � 7
y � �4��3� � 7
y � �4x � 7
x � �3
�185
x �545
�4x � �25
x �545
�4x � 7 � �25
x �195
y � �25
x �195
y � �4x � 7
↔AC.
↔AB
The coordinates of C are
47.
The line containing has slope and passes through
The line containing has slope and passes through
—CONTINUED—
y �53
x �163
y � 2 �53
x �103
y � 2 �53
�x � 2�
y � 2 �53
�x � ��2��
M��2, 2�.
53
BC
y �12
x �132
y � 5 �12
x �32
y � 5 �12
�x � 3�
y � 5 �12
�x � ��3��
L��3, 5�.
12
AB
�53
slope of LN � m3 �5 � 0
�3 � ��6��
�12
�24
slope of MN � m2 �2 � 0
�2 � ��6�
� �3�3
�1slope of LM � m1 �
5 � 2�3 � ��2�
�7, 1�.
y � 1
y �72
�52
y �12
� 7 �52
y �12
x �52
x � 7
9x � 63
5x � �4x � 63
5x � 25 � �4x � 38
12
x �52
��25
x �195
y �12
x �52
y � �25
x �195
MCRBG-0504-SK.qxd 5-25-2001 11:08 AM Page 97
Chapter 5 continued
47. —CONTINUED—
The line containing has slope and passes through
To find A, find the intersection of and
The coordinates of A are
To find B, find the point of intersection of and
The coordinates of B are �1, 7�.
y � 7
y �142
y �12
�132
y �12
� 1 �132
y �12
x �132
x � 1
�7x � �7
3x � 10x � 7
3x � 39 � 10x � 32
12
x �132
�53
x �163
y �53
x �163
y �12
x �132
↔BC.
↔AB
��7, 3�.
y � 3
y � 21 � 18
y � �3��7� � 18
y � �3x � 18
x � �7
72
x ��49
2
12
x � �3x �492
12
x �132
� �3x � 18
y � �3x � 18
y �12
x �132
↔AC.
↔AB
y � �3x � 18
y � �3�x � 6�
y � 0 � �3�x � ��6��
N��6, 0�.�3AC
To find C, find the intersection of and
The coordinates of C are
48.
The line containing has slope 4 and passes through
The line containing has slope and passes through
The line containing has slope and passes through
—CONTINUED—
y � �16
x �73
y � 1 � �16
x �86
y � 1 � �16
�x � 8�
N�8, 1�.
�16
AC
y � �x � 14
y � 5 � �x � 9
y � 5 � �1�x � 9�
M�9, 5�.�1BC
y � 4x � 6
y � 6 � 4x � 12
y � 6 � 4�x � 3�
L�3, 6�.AB
� �1�5
�5Slope of LN � m3 �
6 � 13 � 8
� 4�41
Slope of MN � m2 �5 � 19 � 8
� �16
�1
�6Slope of LM � m1 �
6 � 53 � 9
��5, �3�.
y � �3
y � 15 � 18
y � �3��5� � 18
y � �3x � 18
x � �5
�14
3x �
703
�3x �53
x �703
�3x � 18 �53
x �163
y �53
x �163
y � �3x � 18
↔BC.
↔AC
98 GeometryChapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
MCRBG-0505-SK.qxd 6-14-2001 11:40 AM Page 98
Geometry 99Chapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
Chapter 5 continued
48. —CONTINUED—
To find A, find the point of intersection of and
The coordinates of A are
To find B, find the point of intersection of and
The coordinates of B are
To find C, find the point of intersection of and
The coordinates of C are �14, 0�.
y � 0
y � �14 � 14
y � �x � 14
x � 14
56
x �353
�16
x � �x �353
�16
x �73
� �x � 14
y � �x � 14
y � �16
x �73
↔BC.
↔AC
�4, 10�.
y � 10
y � 16 � 6
y � 4 � 4 � 6
y � 4x � 6
x � 4
5x � 20
4x � �x � 20
4x � 6 � �x � 14
y � �x � 14
y � 4x � 6
↔BC.
↔AB
�2, 2�.
y � 2
y � 8 � 6
y � 4 � 2 � 6
y � 4x � 6
x � 2
256
x �253
4x � �16
x �253
4x � 6 � �16
x �73
y � �16
x �73
y � 4x � 6
↔AC.
↔AB
49.
undefined
is vertical.
The line containing has slope and passes through
The line containing is a vertical line passing through
The line containing has slope and passes through
To find A, find the point of intersection of and
The coordinates of A are
—CONTINUED—
�6, �4�.
y � �4
y � �23
� 6
y � �23
x
x � 6
�43
x � �8
�23
x �23
x � 8
y �23
x � 8
y � �23
x
↔AC.
↔AB
y �23
x � 8
y � 6 �23
x � 2
y � ��6� �23
�x � 3�
N�3, �6�.
23
AC
x � 0
M�0, �4�.BC
y � �23
x
y � 2 � �23
x � 2
y � ��2� � �23
�x � 3�
L�3, �2�.
�23
AB
LN
�40
�slope of LN � m3 ��2 � ��6�
3 � 3
� �23
�2
�3slope of MN � m2 �
�4 � ��6�0 � 3
�23
slope of LM � m1 ��2 � ��4�
3 � 0
MCRBG-0505-SK.qxd 6-14-2001 11:40 AM Page 99
Chapter 5 continued
49. —CONTINUED—
To find B, find the point of intersection of and
The coordinates of B are
To find C, find the point of intersection of and
The coordinates of C are
Lesson 5.6
5.6 Guided Practice (p. 305)
1. An indirect proof might also be called a proof by contra-diction because in an indirect proof, you prove that astatement is true by first assuming that its opposite istrue. If this assumption leads to a contradiction, then youhave proved that the original statement is true.
2. To use an indirect proof to show that two lines m and nare parallel, you would first make the assumption thatlines m and n are not parallel.
3. 4. 5.
6. In if you wanted to prove that youwould use the two cases and in anindirect proof.
5.6 Practice and Applications (pp. 305–307)
7. 8. 9.
10. 11. 12.
13. 14. 15.
16. The correct answer is C because and so by the Converse of the Hinge Theorem
17. The correct answer is B because and so by the Hinge Theorem AC > BD.m�3 < m�5
AD � AD,AB � DC,
m�4 < m�5.AC > AB
AD � AD,BD � CD,
m�1 > m�2UT > SVAB > CB
m�1 < m�2m�1 � m�2XY > ZY
m�1 > m�2m�1 � m�2RS < TU
BC � ACBC < ACBC > AC,�ABC,
DC < FEKL < NQm�1 > m�2
�0, �8�.
y � �8
y � 0 � 8
y �23
� 0 � 8
y �23
x � 8
x � 0
y �23
x � 8
↔BC.
↔AC
�0, 0�.
y � 0
y � �23
� 0
y � �23
x
x � 0
y � �23
x
↔BC.
↔AB
18. because
19. because
20. because
21. Given that and assume that
22. Given with Q the midpoint of assume isnot a median.
23. Given with assume
24. C Assume that there are two points, P and Q, where mand n intersect.
B Then there are two lines (m and n) through points Pand Q.
A But this contradicts Postulate 5, which states that thereis exactly one line through any two points.
D It is false that m and n can intersect in two points, sothey must intersect in exactly one point.
25. Case l: Assume that If one side of a triangleis longer than another side, then the angle oppo-site the longer side is larger than the angle oppo-site the shorter side, so But thiscontradicts the given information that
Case 2: Assume that EF � DF. By the Converse of theBase Angles Theorem, But thiscontradicts the given information that
Since both cases produce a contradiction, the assumptionthat EF is not greater than DF must be incorrect and
26. Assume Then m and n intersect in a point and thetriangle shown in the diagram is formed.
by the Triangle SumTheorem. Then by theSubtraction property of equality. But
because and are supple-mentary. So by the Substitutionproperty of equality. Then by simplifying bothsides. But this is not possible; angle measures in a trian-gle cannot be zero.
So the assumption that must be false. Therefore,m � n.
m � n
m�3 � 0180� � 180� � m�3
�2�1m�1 � m�2 � 180�
� m�3m�1 � m�2 � 180�m�1 � m�2 � m�3 � 180�
m � n.
EF > DF.
m�D > m�E.
m�E � m�D.
m�D > m�E.
m�D < m�E.
EF < DF.
m�C � 90�.m�A � m�B � 90�,�ABC
MQNP,�MNP
RS � 7 in.ST � 5 in.,RS � ST � 12 in.
x < 17.5
4x < 70
2 < 4.�4x � 5�� < 65�
x > 1
2x > 2
3x > x � 2
115� > 45�.3x � 1 > x � 3
70� > 60�.x > 9
100 GeometryChapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
MCRBG-0505-SK.qxd 6-14-2001 11:40 AM Page 100
Geometry 101Chapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
Chapter 5 continued
27. Case 1: Assume that Then bythe Converse of the Hinge Theorem. But
by the ASA CongruencePostulate, so �S � �T or This is a contradiction. So RS ≤ RT.
Case 2: Assume Then by the Converse of the Hinge Theorem. But
by the ASA CongruencePostulate, so or This is a contradiction. So
Therefore and is an isosceles triangle.
28. The paths are described by two triangles in which twosides of one triangle are congruent to two sides of anoth-er triangle, but the included angle in your friend’s triangleis larger than the included angle of your triangle, so theside representing the distance from the airport is longer inyour friend’s triangle.
29. The paths are described by two triangles in which twosides of one triangle are congruent to two sides of anoth-er triangle, but the included angle in your friend’s triangleis larger than the included angle in your triangle, so theside representing the distance to the airport is longer inyour friend’s triangle.
30. a. As ED increases, increases because ∠EBD isthe angle opposite
As ED increases, decreases because increases and and are supplementary.
b. As ED increases, AD decreases because as EDincreases increases and decreasesmaking AD decrease.
c. The cleaning arm illustrates the Hinge Theorembecause the lengths of and remain constantwhile and ED change. In �EBD and �ABD,
The included angle in �EBD,�EBD, is larger than the included angle in �ABD,�ABD. So is longer than .ADED
BE � BD � BA.m�EBD
BDBE
m�ABDm�EBD
�EBD�DBAm�EBDm�DBA
ED.m�EBD
�RST RS � RT
RS ≥ RT.m�S � m�T.�S � �T
�RUS � �RUT
m�T < m�SRS < RT.
m�S � m�T.�RUS � �RUT
m�T > m�SRS > RT. 31.
Statements Reasons
1. 1. Given
2. Construct a ray from B 2. Protractor Postulateto construct an angle in the interior of that is congruent to
.
3. Locate P on the con- 3. Ruler Postulate structed ray such that
.
4. 4. SAS Congruence Postulate
5. 5. Corresponding parts of congruent triangles arecongruent
6. Locate H on so 6. Protractor Postulatethat BHxxxy bisects .
7. 7. Definition of angle bisec-tor
8. 8. Transitive property of congruence (Steps 1, 3)
9. 9. Reflexive property of congruence
10. 10. SAS Congruence Postulate
11. 11. Corresponding parts ofcongruent triangles arecongruent
12. 12. Definition of congruentsegments
13. 13. Segment AdditionPostulate
14. 14. Substitution property ofequality
15. 15. Triangle Inequality
16. 16. Substitution property ofequality
17. 17. Definition of congruentsegments (Step 5)
18. 18. Substitution property ofequality
AC > DF
PC � DF
AC > PC
PH � HC > PC
AC � PH � HC
AC � AH � HC
AH � PH
AH � PH
�ABH � �PBH
BH � BH
PB � AB
�PBH � �ABH
�PBAAC
PC � DF
�PBC � �DEF
BP � ED
�DEF
�ABC
m�ABC > m�DEFAB � DE, BC � EF,
MCRBG-0505-SK.qxd 6-14-2001 11:40 AM Page 101
Chapter 5 continued
5.6 Mixed Review (p. 308)
32. isosceles 33. equilateral, equiangular, and isosceles
34. scalene 35. isosceles
36. equiangular, equilateral, and isosceles
37. isosceles
38.
39.
41.
42. is a median, an altitude, anangle bisector, and a perpendicular bisector. divides intotwo congruent triangles. It is short-er than each side of .
5.6 Quiz 2 (p. 308)
1. 2. If then
3. If the perimeter of then the perimeter of
4.
5.
6.
MP, NP, MN
m�M � 57�
m�M � 123� � 180�
m�M � 48� � 75� � 180�
m�M � m�N � m�P � 180�
MQ, MP, PQ
m�M � 81�
m�M � 99� � 180�
m�M � 49� � 50� � 180�
m�M � m�P � m�Q � 180�
LQ, LM, MQ
m�M � 31�
m�M � 149� � 180�
75� � m�M � 74� � 180�
m�L � m�M � m�Q � 180�
�GHF � 21�CDE � 42,
CE � 16.FG � 8,FG � CE
�RST
�RSTRU
RU
R S
T
U
m�BAC � 84�
m�BAC � 96� � 180�
m�BAC � 51� � 45� � 180�
m�BAC � m�B � m�C � 180�
m�B � 51�
m�B � 32� � 19�
m�B � �x � 19��
32 � x
2x � 32 � 3x
�x � 13�� � �x � 19�� � 3x�
7. is longer than because two sides of arecongruent to two sides of and the included angle
is larger than included angle so
8. The 2nd Group is farther from the camp because thegroups’ paths form two triangles with 2 pairs of congruent sides and the included angle for the 2nd groupis larger than the included angle for the 1st group.
Review (pp. 310–312)
1. If a point is on the perpendicular bisector of a segment,then it is equidistant from the endpoints of the segment.
2. If then U must be on the perpendicular
bisector of
3. If Q is equidistant from and then Q is on thebisector of
4. Let X be the midpoint of Then oror
But because K is equidistant from R, S,and T.
5.
Since W is equidistant from the sides of
6. The special segments are angle bisectors and the point of concurrency is the incenter
7. The special segments are perpendicular bisectors and the point of concurrency is the circumcenter.
8. The special segments are medians and the point of concurrency is the centroid.
9. The special segments are altitudes and the point of concurrency is the orthocenter.
WB � WA � 6.�XYZ,
WA � 6
�WA�2 � 36
�WA�2 � 64 � 100
�WA�2 � 82 � 102
�WA�2 � �AY�2 � �WY�2
KR � KT � 20
20 � KT
400 � KT 2
144 � 256 � KT 2
122 � 162 � KT 2
�KX�2 � �XT�2 � �KT�2
XT � 16.XT �12 � 32
XT �12 STST.
�RST.
→ST,
→SR
RT.↔SQ
UR � UT,
DE > AB.�BCA�DFE�DEF
�ABCABDE
102 GeometryChapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
40.
m�C � 45�
m�C � 32� � 13�
m�C � �x � 13��
MCRBG-0505-SK.qxd 6-14-2001 11:40 AM Page 102
Geometry 103Chapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
Chapter 5 continued
10. midpoint of
midpoint of
midpoint of
An equation of the median to XZ___
is
.
An equation of the median to YZ___
is
.
The centroid is the point of intersection of the two lines.
The coordinates of the centroid of are ��43
, 2�.�XYZ
y � 2
y � �32 ��
43�
y � �32
x
�43
� x
3 ��94
x
34
x � 3 ��32
x
y � �32
x
y �34
x � 3
y � �32
x
y � 0 � �32
�x � 0�
m2 �3 � 0
�2 � 0�
3�2
y �34
x � 3
y �34
�x � 4�
y � 0 �34
�x � ��4��
m1 �3 � 0
0 � ��4� �34
� ��2, 3�
� ��42
, 62�
YZ � ��4 � 02
, 0 � 6
2 �
� �0, 3�� �02
, 62�XZ � �0 � 0
2,
6 � 02 �
� ��2, 0�
� ��42
, 02�
XY � ��4 � 02
, 0 � 0
2 � 11. The coordinates of the orthocenter of are since is a right triangle and the two legs are alsoaltitudes of
12. The slope of
The slope of
The slope of
The line containing has slope and passes through.
The line containing has slope 1 and passes through.
The line containing has slope 0 and passes through.
H is the point of intersection of and
The coordinates of H are
J is the point of intersection of and
The coordinates of J are
—CONTINUED—
�10, 1�.
10 � x
�10 � �x
1 � �x � 11
y � 1
y � �x � 11
↔JK.
↔HJ
�6, 5�
y � 5
y � �6 � 11
y � �x � 11
x � 6
�2x � �12
�x � x � 12
�x � 11 � x � 1
y � x � 1
y � �x � 11
↔HK.
↔HJ
y � 1.
y � 1 � 0
y � 1 � 0�x � 6�
N�6, 1�JK
y � x � 1.
y � 3 � x � 4
y � 3 � 1�x � 4�
L�4, 3�HK
y � �x � 11.
y � 3 � �x � 8
y � 3 � �1�x � 8�
M�8, 3��1HJ
LN � m3 �3 � 14 � 6
�2
�2� �1
MN � m2 �3 � 18 � 6
�22
� 1
LM � m1 �3 � 38 � 4
�04
� 0
�XYZ.�XYZ
�0, 0��XYZ
Geometry 103Chapter 5 Worked-out Solution Key
MCRBG-0506-SK.qxd 5-25-2001 11:21 AM Page 103
Chapter 5 continued
12. —CONTINUED—
K is the point of intersection of and
The coordinates of K are
13. Let L be the midpoint of M be the midpoint of and N be the midpoint of
The slope of the slope of so
The slope of the slope of so
The slope of the slope of so
14.
16. The angle measurements in order from least to greatestare and The side measurements inorder from least to greatest are AB, BC, and AC.
17. The angle measurements in order from least to greatestare and The side measurements inorder from least to greatest are EF, DF, and DE.
18.
The angle measurements in order from least to greatestare and The side measurements inorder from least to greatest are GJ, GH, and HJ.
19.
The angle measurements in order from least to greatestare and The side measurements inorder from least to greatest are KM, LM, and KL.
m�M.m�L, m�K,
m�L � 35�
m�L � 55� � 90�
m�L � m�K � 90�
m�G.m�H, m�J,
m�J � 60�
m�J � 120� � 180�
m�J � 50� � 70� � 180�
m�J � m�H � m�G � 180�
m�F.m�D, m�E,
m�B.m�C, m�A,
P � 64
P � 18 � 22 � 24
P � BC � CD � BD
24 � BD
12 �12 BD
GF �12 BD
18 � BC
9 � 9 � BC
BG � GC � BC
BG � GC � 9
LN � JK.JK,LN � �1 �
MN � HJ.HJ,MN � 1 �
LM � HK.HK,LM � 0 �
HK.JK,HJ,
�2, 1�.
2 � x
1 � x � 1
y � 1
y � x � 1
↔JK.
↔HK
20. The length of the third side must be less than the sum ofthe lengths of the other two sides. So the length of thethird side must be less than 300 feet So themaximum length of fencing needed is 600 feet
of fencing.
21. 22. 23.
24. In if then .
25. Assume has two right angles at and Thenand, since
This contradicts theTriangle Sum Theorem. Then the assumption that there issuch a must be incorrect and no triangle has tworight angles.
Chapter 5 Test (p. 313)
1. If P is the circumcenter of then PR, PS, and PTare always equal.
2. If bisects then and are sometimescongruent.
3. The incenter of a triangle never lies outside the triangle.
4. The length of a median of a triangle is sometimes equal tothe length of a midsegment.
5. If is the altitude to side of then isalways shorter than
6. a.
b.
c.
d.
BC � 19.8
BC � 9.9 � 9.9
BC � CF � FB
HE � 5
23 HE �103
HE �13 HE �
103
HE �13 �HE � 10�
HE �13 �HE � HB�
HE �13 EB
10 � HB
100 � �HB�2
36 � 64 � �HB�2
62 � 82 � �HB�2
�HG�2 � �GB�2 � �HB�2
HC � 12
13 HC = 4
HC �23 HC � 4
HC �23 �HC � 6�
HC �23 �HC � HG�
HC �23 CG
AB.AM�ABC,BCAM
CDAD�ABC,→BD
�RST,
�ABC
m�A � m�B � m�C > 180�.m�C > 0�,m�A � m�B � 180�
�B.�A�ABC
MP ≠ QP�M � �Q,�MPQ,
TU � VSm�1 < m�2AB < CB
�100 � 200 � 300�
�100 � 200�.
104 GeometryChapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
15.
P � 31
P � 9 � 12 � 10
P � ST � TU � SU
TU � 12
TU �12 � 24
TU �12 PQ
ST � 9
ST �12 � 18
ST �12 RQ
18 � RQ
9 � 9 � RQ
RU � UQ � RQ
RU � UQ � 9
MCRBG-0506-SK.qxd 5-25-2001 11:21 AM Page 104
Geometry 105Chapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
Chapter 5 continued
7. Point H is the centroid of the triangle.
8. is a(n) median, perpendicular bisector, altitude, andangle bisector of
9. and by the Midsegment Theorem.
10. because the side opposite islonger than the side opposite
11. To locate the pool so that its center is equidistant fromthe sidewalks, find the incenter of the triangle by con-structing angle bisectors of two angles of the triangle andlocating the point of intersection of the bisectors. Thispoint will be equidistant from each sidewalk.
12. The converse of the Hinge Theorem guarantees that theangles between the legs get larger as the legs are spreadapart.
13. The maximum distance between the end of two legs is 10 feet because the length of the third side of the trianglemust be less than the sum of the lengths of the other twosides.
14.
If then is longer than because two sides of one triangle are congruent to twosides in another triangle and the measure of the includedangle of one triangle is larger than the measure of theincluded angle of the other triangle (Hinge Thm.).
15.
Statements Reasons
1. 1. Given
2. 2. Segment Addition Post.
3. 3. Substitution property of equality
4. 4. Triangle Inequality Theorem
5. 5. Substitution property ofequality
16. Assume Then because iftwo angles of a triangle are congruent, then the sidesopposite them are congruent. So by the defini-tion of congruent segments. But this contradicts the givenstatement that Therefore, the assumption mustbe false. So m�D � m�ABC.
AD � AB.
AD � AB
AD � ABm�D � m�ABC.
BE < AE
BE < BC � CE
BC � CE � AE
AC � CE � AE
AC � BC
BCACm�AOC > m�BOC,
A BC
O
�ACB.�BACm�BAC > m�ACB
EF � ABEF �12 AB
�ABC.CG
Chapter 5 Standarized Test (pp. 314–315)
1. 2. D 3. B
B
4. The midpoint of is
The centroid is two thirds of the distance from each vertex to the midpoint of the opposite side.
But
So
The coordinates of C are or
E
5. so
so
So
C
6. A
7. The length of the side has to be greater than or12 inches and less than inches. A
8. A
9. because the sum of the measures of the acuteangles of a right triangle is 90�.x � y � 90
28 � 16 � 4428 � 16
P � 48
P � 12 � 16 � 20
P � NP � PL � NL
20 � NL
400 � �NL�2
144 � 256 � �NL�2
122 � 162 � �NL�2
�NP�2 � �PL�2 � �NL�2
NP � 12MK � 12,
PL � 16KP � 16,
��7, �3�.��7, �11 � 8�
CH � 8
CH �23 � 12
CH �23 MH
MH � 1 � ��11� � 12.
CH �23 MH
� ��7, 1�.
� ��142
, 22�
M � ��12 � ��2�2
, 1 � 1
2 �FG
y � 4
�12 y � �2
92 y � 5y � 2
92 y � 4 � 5y � 6
x � 9
103 x � 30
4x �23 x � 30
4x � 9 �23 x � 21
MCRBG-0506-SK.qxd 5-25-2001 11:21 AM Page 105
Chapter 5 continued
10. because the side opposite is longer than theside opposite
11. If then But so C
12. The location of the point of intersection of the perpendic-ular bisectors is the midpoint of because is aright triangle.
13. Let M be the midpoint of
Let N be the midpoint of
Let P be the midpoint of
The slope of
An equation of is
The slope of
An equation of is
The slope of
An equation of is
The centroid is the point of intersection of and
The coordinates of the centroid are �10, 2�.
y � 2
y �15
� 10
y �15
x
x � 10
�95
x � �18
15
x � 2x � 18
y � 2x � 18
y �15
x
↔CM.
↔AN,
↔PB,
y � �14
x �92
y � 0 � �14
�x � 18�↔CM
� �14
�3
�12↔CM � m3 �
3 � 06 � 18
y � 2x � 18
y � 0 � 2�x � 9�↔BP
↔BP � m2 �
6 � 012 � 9
�63
� 2
y �15
x
y � 0 �15
�x � 0�↔AN
�15
�3
15↔AN � m1 �
3 � 015 � 0
� �9, 0�� �182
, 02�P � �0 � 18
2,
0 � 02 �
AC.
� �15, 3�� �302
, 62�N � �12 � 18
2,
6 � 02 �
BC.
� �6, 3�� �122
, 62�M � �0 � 12
2,
0 � 62 �
AB.
�GHJGH
x > 45.x > yx � 45.x � y,
�H.�Gx� > y�
14. The slope of
The slope of the line perpendicular to is undefined.
So the line perpendicular to that passes through B isthe line
The slope of
The slope of the line perpendicular to is because
An equation of the line perpendicular to and passingthrough is
The slope of
The slope of the line perpendicular to is 1 because
An equation of the line parallel to and passingthrough is
The orthocenter is the point of intersection of
and
The coordinates of the orthocenter are
15. a. The coordinates of the centroid are The coor-dinates of the orthocenter are Find the equa-tion of the line passing through the centroid and the orthocenter then show that the cir-cumcenter is also on the line.
An equation of the line passing through the centroidand the orthocenter is
Substitute the coordinates of the circumcenter intothis equation.
—CONTINUED—
y � 5x � 48
y � 2 � 5x � 50
y � 2 � 5�x � 10�
slope � m �12 � 2
12 � 10�
102
� 5
�9, �3��12, 12�,
�10, 2��12, 12�.
�10, 2�.
�12, 12�.
y � 12
y � �24 � 36
y � �2 � 12 � 36
y � �2x � 36
x � 12
↔CP.
↔BM,
↔AN,
y � x.
y � 0 � 1�x � 0�A�0, 0�
↔BC
1 � ��1� � �1.
↔BC
�6
�6� �1.
↔BC � m3 �
6 � 012 � 18
y � �2x � 36.
y � 0 � �2�x � 18�C�18, 0�
↔AB
12
� ��2� � �1.
�2↔AB
�6
12�
12
↔AB � m2 �
6 � 012 � 0
x � 12.
↔AC
↔AC
↔AC � m1 �
0 � 018 � 0
�0
18� 0
106 GeometryChapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
MCRBG-0506-SK.qxd 5-25-2001 11:21 AM Page 106
Geometry 107Chapter 5 Worked-out Solution Key
Copyright © McDougal Littell Inc. All rights reserved.
Chapter 5 continued
15. —CONTINUED—
Since is true, the circumcenter is on thesame line as the centroid and the orthocenter.Therefore, they are all collinear.
b. The distance from the circumcenter C to the centroidD is CD.
The distance from the circumcenter C to the orthocenter P is CP.
So the distance from the circumcenter to the centroidis one third the distance from the circumcenter to theorthocenter.
Project Chapters 4–5 (pp. 316–317)
Investigation
1. The lines are medians because they are the lines that con-tain the line segments whose endpoints are a vertex of thetriangle and the midpoint of the opposite side.
2. The balancing point of the triangle is the centroid becauseit is the point of intersection of the medians.
3. Answers will vary.
4. Conjecture: The balancing point of a square, a rectangle, a parallelogram, or a rhombus is the point ofintersection of its diagonals.
5. Answers will vary.
Sample answer: I tested the conjecture by making moreexample shapes of each kind. The results were the sameeach time. The balancing point was the point of intersec-tion of the diagonals.
�26 � �26
�26 �13
�3�26�
CD �13
CP
� 3�26
� �9�26
� �234
� �9 � 225
� �32 � 152
CP � ��12 � 9�2 � �12 � ��3��2
� �26
� �1 � 25
� �12 � 52
CD � ��10 � 9�2 � �2 � ��3��2
�3 � �3
�3 � �3
�3 � 45 � 48
�3 � 5 � 9 � 48
Present Your Results
Projects may vary.
Extension
The conjecture does not work for all four–sided shapes. Thefollowing is an example for which it was not true.
MCRBG-0506-SK.qxd 5-25-2001 11:21 AM Page 107