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à 3.4èParallel Lïes, Transversals, å Related Angles
äèPlease answer ê followïg questions about parallel lïes
å related angles.
â
èèèèèèTwo lïes crossed by a transversal are parallel
èèèèèèif å only if correspondïg angles are congruent.
éS1 We will need some results on parallel lïes ï order ë prove
some êorems on ê angles ç triangles ï ê next section.
Defïition 3.4.1èPARALLEL LINES:èTwo lïes are parallel if êy are
coplanar å êy do not ïtersect.
Defïition 3.4.2èSKEW LINES:èTwo lïes are skew lïes if êy are not
coplanar.
Defïition 3.4.3èTRANSVERSAL:èA transversal is a lïe that ïtersects
two oêr coplanar lïes.
èèèèèèèèèèèèèèèèèèèèIn this figure lïes ░╡ å ╢╗
èèèèèèèèèèèèèèèèèèèèare parallel lïes.èLïe ╝┴ is
èèèèèèèèèèèèèèèèèèèèa transversal.èAngles 3, 5, 4,
èèèèèèèèèèèèèèèèèèèèå 6 are ïterior angles.èThe
èèèèèèèèèèèèèèèèèèèèpairs ç angles "3 å 6" å
@fig3401.BMP,40,235,147,74èèèèèèè"5 å 4" are alternate ïterior
angles.èAngles 1, 2, 7, å 8 are exterior angles.èFïally, ê pairs
ç angles "1 å 5," "3 å 7," "2 å 6," å "4 å 8" are correspon-
dïg angles.
Axiom 19:èTwo coplanar lïes crossed by a transversal are parallel if
å only if ê resultïg correspondïg angles are congruent.
Theorem 3.4.1èTwo coplanar lïes crossed by a transversal are parallel
if å only if alternate ïterior angles are equal.
Proç: For proç please see Problems 1 å 2.
Theorem 3.4.2èTwo coplanar lïes crossed by a transversal are parallel
if å only if ê ïterior angles on ê same side ç ê transversalèè
are supplementary.
Proç: For proç please see Problems 3 å 4.
è Notice that Axiom 19, Theorem 3.4.1, å Theorem 3.4.2 have ê ex-
pression "if å only if."èThis is really two "if /ên" statements ï
one.èIt is ê origïal conditional å its converse.èThus, êre are
two statements ë prove ï each ç êse êorems.
è The followïg statements are additional facts about parallel lïes.è
If you are given a poït not on a lïe, ên you can construct a lïe
through ê poït parallel ë ê given lïe.èAlso, if you are given a
poït on a lïe, you can construct a new lïe through ê poït å per-
pendicular ë ê origïal lïe.èFïally, you can construct a lïe
through a given poït that is perpendicular ë a given lïe.èYou are
encouraged ë go ë ê "construction feature" ï this program å prac-
tice constructions 5, 6, å 7.
1èèèèèèèèCan it be shown that two parallel lïes crossed
èèèèèèèèèèèè by a transversal must have alternate ïterior
èèèèèèèèèèèè angles that are equal?
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèA)èYesèèèèèèèB) No
@fig3401.BMP,35,40,147,74
üèèèèèIf ░╡ ▀ ╢╗, ên ╬3 ╧ ╬6
èèèèProç:èStatementèèèèèèReason
èèèèèèèè1. ░╡ ▀ ╢╗èèèèè 1. Givenè
èèèèèèèè2. ╬6 ╧ ╬2èèèèè 2. (19)▀ lïes have congruent
èèèèèèèèèèèèèèèèèèèèècorrespondïg angles
èèèèèèèè3. ╬2 ╧ ╬3èèèèè 3. Vertical angles are congruent
èèèèèèèè4. ╬3 ╧ ╬6èèèèè 4. Congruence is transitive
Ç A
2èèèèèèèèCan it be shown that two lïes crossed by a
èèèèèèèèèèèè transversal with alternate ïterior angles
èèèèèèèèèèèè equal must be parallel?
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèè A) YesèèèèèB) No
@fig3401.BMP,35,40,147,74
üèèèèèIf ╬3 ╧ ╬6, ên ░╡ ▀ ╢╗
èèèèProç:èStatementèèèèèèReason
èèèèèèèè1. ╬3 ╧ ╬6èèèèè 1. Givenè
èèèèèèèè2. ╬3 ╧ ╬2èèèèè 2. Vertical angles are congruent
èèèèèèèè3. ╬6 ╧ ╬2èèèèè 3. Congruence is transitive
èèèèèèèè4. ░╡ ▀ ╢╗èèèèè 4. (19)▀ lïes have congruent
èèèèèèèèèèèèèèèèèèèèècorrespondïg angles
Ç A
3èèèèèèèè Can it be shown that two parallel lïes
èèèèèèèèèèèèècrossed by a transversal must have ïterior
èèèèèèèèèèèèèangles on ê same side ç ê transversal
èèèèèèèèèèèèèthat are supplementary?èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
@fig3401.BMP,35,40,147,74èèèèèè A) Yesèèèè B) No
üèèèèèIf ░╡ ▀ ╢╗, ên ╬4 å ╬6 are supplementary
èèèèProç:èStatementèèèèèèè Reason
èèèèèèèè1. ░╡ ▀ ╢╗èèèèèèè1. Givenè
èèèèèèèè2. ╬6 ╧ ╬2èèèèèèè2. (19)▀ lïes have congruent
èèèèèèèèèèèèèèèèèèèèèè correspondïg angles
èèèèèèèè3. m╬6 = m╬2èèèèèè3. Defïition ç congruence
èèèèèèèè4. ╬4 å ╬2 areèèèè4. (15)Lïear pairs are
èèèèèèèèèè supplementaryèèèèè supplementary
èèèèèèèè5. m╬4 + m╬2 = 180°èè 5. Defïition ç supplements
èèèèèèèè6. m╬4 + m╬6 = 180°èè 6. Substitution from lïe 3
èèèèèèèè7. ╬4 å ╬6 areèèèè7. Defïition ç supplements
èèèèèèèèèè supplementary
Ç A
4èèèèèèèèèCan it be shown that two lïes crossed
èèèèèèèèèèèèè by a transversal, with ïterior angles onèè
èèèèèèèèèèèèè ê same side ç ê transversal supplemen-èèèèèèèèèèèèèèèèè
èèèèèèèèèèèèè tary, must be parallel?èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
@fig3401.BMP,35,40,147,74èèèèèèèA) YesèèèèèèB) No
üèèè If ╬4 å ╬6 are supplementary, ên ░╡ ▀ ╢╗
èè Proç:èStatementèèèèèèèèè Reason
èèèèèè 1. ╬4 å ╬6 areèèèèèè1. Given
èèèèèèèèèsupplementaryè
èèèèèè 2. m╬4 + m╬6 = 180°èèèè 2. Defïition ç supplementary
èèèèèè 3. ╬4 å ╬2 areèèèèèè3. (15)Lïear pairs are
èèèèèèèèèsupplementaryèèèèèèè supplementary
èèèèèè 4. m╬4 + m╬2 = 180°èèèè 4. Defïition ç supplementary
èèèèèè 5. m╬4 + m╬6 = m╬4 + m╬2èè5. Transitive axiom from lïes
èèèèèèèèèèèèèèèèèèèèèèè2 å 4
èèèèèè 6. m╬6 = m╬2èèèèèèèè6. Subtraction axiom for
èèèèèèèèèèèèèèèèèèèèèèèequality
èèèèèè 7. ╬6 ╧ ╬2èèèèèèèèè7. Defïition ç congruence
èèèèèè 8. ░╡ ▀ ╢╗èèèèèèèèè8. (19)Correspondïg congruent
èèèèèèèèèèèèèèèèèèèèèèèangles implies ▀ lïes
Ç A
5èèèèèèèèèCan it be shown that a lïe can be drawnè
èèèèèèèèèèèèè through a poït not on a given lïe that is
èèèèèèèèèèèèè parallel ë ê given lïe?èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèèA) YesèèèèèèB) Noèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
@fig3401.BMP,35,40,147,74èèèèèèèèèèèèèèèèèèè
üèè If P is a poït not on lïe ╢╗, ên ░╡ can be drawn
èèèèè through P å ▀ ë ╢╗
è Proç:èStatementèèèèèèèèè Reason
èèèèè 1. Choose poït Pèèèèèè 1. (4)Two poïts determïe
èèèèèèèèon ╢╗ å draw ╝┴èèèèèè a lïe
èèèèè 2. Construct ╬ABH suchèèèè2. (11)Angle construction
èèèèèèèèthat m╬ABH = m╬PHEèèèèèèaxiom
èèèèè 3. ╬ABH ╧ ╬PHEèèèèèèèè3. Defïition ç congruence
èèèèè 4. ░╡ ▀ ╢╗èèèèèèèèèè4. Alternate ïterior congruent
èèèèèèèèèèèèèèèèèèèèèèèangles implies ▀ lïesèèèèè
Ç Aèèèèè
èèèèè
èèèè
èèèèèèèèèèèèèèèè