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GEOMETRY
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CHAPTER1.6Y
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à 1.6èDefïitions å Axioms for Angles
äèPlease answer ê followïg questions about angular
measurement.
â
èè The measure ç an angle is represented uniquely by exactly one
èè real number b, called its degree measure, with 0 ≤ b ≤ 180.
éS1 We will see that ê process ç measurïg angles is similar ë
ê process ç measurïg segments.èThus, ï ê material that follows,
ê defïitions å axioms for angles will be similar ë ê defïitions
å axioms for segments.
è An angle like a poït, segment, ray, lïe, or plane ia a geometric
figure.èThey are all collections ç poïts.èA ray is a collection ç
poïts, å an angle is ê union ç two rays.
Defïition 1.6.1èANGLE:èAn angle is ê union ç two rays that share
a common endpoït.
è The rays ç an angle are called ê sides ç ê angle, å ê com-
mon endpoït is called ê vertex ç ê angle.èWe will use ê nota-
tion m ╬ABC ë mean ê measure ç ╬ABC.
èèèèèèèèèèèèèèèèèèè In this figure, ê sides ç ê
èèèèèèèèèèèèèèèèèèè angle are ┤╕ å ┤▓,å ê ver-
èèèèèèèèèèèèèèèèèèè tex is B.èThis angle can be re-
èèèèèèèèèèèèèèèèèèè presented by ê symbols ╬ABC or
èèèèèèèèèèèèèèèèèèè ╬CBA.èThe letter at ê vertex
@fig1601.BMP,65,280,147,74èèèèèè is written ï ê middle.èSome-
times when êre is no confusion, ê angle can be called ╬B or╬3.
è Angles can be measured ï degrees.èIf ê circle is divided ïë 360
equal parts, ên each one ç ê parts is called a degree.èA protrac-
ër can be used ë approximate ê measure ç an angle ï degrees.è
è You are encouraged at this time ë go ë ê measurement feature ï
this program ë practice measurïg angles ï degrees.
Defïition 1.6.2èCONGRUENT ANGLES:èTwo angles are congruent if êy
have ê same measure.
è In measurïg angles, we probably made ê same assumptions that we
made for segments.èWe probably assumed that ê measurement ç an angle
is unique, å that if you place ê ïitial side ç ê angle hori-
zontal, êre is a unique degree measure at ê termïal side ç ê
angle on ê protracër.
è The followïg axioms provide this assurance.
Axiom 10:èThe measure ç an angle is represented uniquely by exactly
one real number called its degree measure.
Axiom 11:èIf you place a protracër on an angle with ê ïitial side at
zero degrees, ên êre is a unique degree measure at ê termïal side
ç ê angle.
è An axiom allows us ë add two angle measures ëgeêr ë get ëtal
measure.
Axiom 12:èIf poït P is ïterior ë ╬ABC, ên ê measure ç ╬ABP plus
ê measure ç ╬PBC equals ê measure ç ╬ABC.
Defïition 1.6.3èANGLE BISECTOR:èAn angle bisecër is a ray ïterior
ë ╬ABC that divides ê angle ïë two angles with equal measures.
Axiom 13:èThe angle bisecër ç a given angle is unique.
è You are encouraged at this time ë go ë ê "construction feature" ç
this program å practice constructions (3) å (4).èConstruction (3)
ïvolves constructïg an angle congruent ë a given angle, å construc-
tion (4) ïvolves constructïg an angle bisecër ç a given angle.
è Sometimes it is necessary ë measure angles with great precision.è
For this purpose, ê degree is divided ïë 60 equal parts called mï-
utes, å one mïute is divided ïë 60 equal parts called seconds.èFor
example, 35°20'42" is read 35 degrees, 20 mïutes, å 42 seconds.
1
èèèèèèèèèèèèèèèèèèèè If m╬DEC = 60° å m╬CEB = 60°,è
èèèèèèèèèèèèèèèèèèèè fïd m╬DEB.
èèèèèèèèèèèèèèèèèèèèèèA)è120°èèèè B)è5°èèèèèèèèèèè
@FIG1602.BMP,35,40,147,74èèèèèèèèè C)è85°èèèèèD)èNone
ü
èèèèèèèèèè m╬DEC + m╬CEB = 60° + 60° = 120°
Ç A
2
èèèèèèèèèèèèèèèèèèèèIf m╬AEC = 120° å m╬BEC = 60°,è
èèèèèèèèèèèèèèèèèèèèfïd m╬AEB.
èèèèèèèèèèèèèèèèèèèèèèA)è80°èèèèèB) 75°èèèèèèèèèèè
@FIG1602.BMP,35,40,147,74èèèèèèèèè C)è60°èèèèèD)èNone
ü
èèèèèèèèèèèm╬AEC - m╬BEC = 120° - 60° = 60°
Ç C
3
èèèèèèèèèèèèèèèèèèèèèè Fïd m╬AEB + m╬BEC + m╬CED,è
èèèèèèèèèèèèèèèèèèèèèè if ░┴ is a lïe.
èèèèèèèèèèèèèèèèèèèèèèA) 130°èèèèèB) 180°èèèèèèèèèèè
@FIG1602.BMP,35,40,147,74èèèèèèèèè C)è240°èèèè D)èNone
ü
èèèèèèèèèè m╬AEB + m╬BEC + m╬CED = 180°
Ç B
4
èèèèèèèèèèèèèèèèèèèèèè Give anoêr name for ╬2.è
èèèèèèèèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèèèèèA) ╬BECèèèèèB) ╬AECèèèèèèèèèèè
@FIG1602.BMP,35,40,147,74èèèèèèèèè C) ╬BEPèèèèèD) None
ü
èèèèèèèèèèèèèèèèè╬BEC
Ç A
5
èèèèèèèèèèèèèèèèèèèName two angles with ║╡ as a side.è
èèèèèèèèèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèèè A) ╬AEC,╬CEPèèèB) ╬BEC, ╬BEDèèèèèèèèèèè
@FIG1602.BMP,35,40,147,74èèèèèèèèC) ╬CED,╬PEDèèèD)èNone
ü
è There are many angles with ║╡ as a side.èAnswer B has two ç êm.
Ç B
6
èèèèèèèèèèèèèèèèèèèèèIf ║╡ is ê bisecër ç ╬AEC,è
èèèèèèèèèèèèèèèèèèèèèwhat is true ç ╬3 å ╬2?èè
èèèèèèèèèèèèèèèèèèèèè A) ╬3 ≥ ╬2èèèB) ╬3 ≤ ╬2èèèèèèèèèèè
@FIG1602.BMP,35,40,147,74èèèèèèèèèC) ╬3 = ╬2èèèD)èNone
ü
èèèèèèèèèèèèèèèè╬3 = ╬2
Ç C
7
èèèèèèèèèèèèèèèèèèèèèè Is ║└ ê bisecër ç ╬CED?è
èèèèèèèèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèèèèèè A) YesèèèB) Noèèèèèèèèèèè
@FIG1602.BMP,35,40,147,74èèèèèèèèèèèC) Not enough ïformationèèè
ü
èèèèèèèèèèèèNot enough ïformation.
Ç C
8
èèèèèèèèèèèèèèèèèèèèèèèèèm╬3 + m╬2 = m╬______.è
èèèèèèèèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèèèèèèèA) m╬BEPèèèB)èm╬AECèèèèèèèèèèè
@FIG1602.BMP,35,40,147,74èèèèèèèèèèè C) m╬PEDèèèD)èNone
ü
èèèèèèèèèèèèèèm╬3 + m╬2 = m╬AEC
Ç B
9
èèèèèèèèèèèèèèèèèèèèèèè m╬BED - m╬PED = m╬______.è
èèèèèèèèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèèèèèèèA) m╬BEPèèèB)èm╬CEPèèèèèèèèèèè
@FIG1602.BMP,35,40,147,74èèèèèèèèèèè C) m╬AEBèèèD)èNone
ü
èèèèèèèèèèèèè m╬BED - m╬PED = m╬BEP
Ç A
10
èèèèèèèèèèèèèèèèèèèèè m╬AEB = 60°, m╬BEC = 60°, åè
èèèèèèèèèèèèèèèèèèèèè m╬AEP = 150°, fïd m╬CEP.èèèèèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèèèèèèèèA) 30°èèèB)è20°èèèèèèèèèèè
@FIG1602.BMP,35,40,147,74èèèèèèèèèèèè C) 25°èèèD)èNone
ü
èèèèèèèèèèèèè150° - (60° + 60°) = 30°
Ç A
11
èè An angle is ê union ç two rays that share a common _________.èèè
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèA)èSegmentèèèè B)èRayèèèè C)èEndpoïtèèèè D)èNoneèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
ü
èèèèèèèèèèèèèèèèEndpoït
Ç C
12
The common endpoït ç two rays that form an angle is called ê ______.èèè
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèè A)èVertexèèèèB)èRaysèèèèC)èSidesèèèèD)èNoneèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
ü
èèèèèèèèèèèèèèèèèVertex
Ç A
13
èèèèè Two angles are congruent if êy have ê same ______.èèè
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèèA)èVertexèèè B)èSidesèèè C)èMeasureèèè D)èNoneèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
ü
èèèèèèèèèèèèèèèè Measure
Ç C
14
If a ray divides an angle ïë two equal angles, it is called a _______.èèè
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
è A)èVertexèèè B)èBisecërèèèC)èTermïal sideèèèD)èNoneèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
ü
èèèèèèèèèèèèèèèè Bisecër
Ç B