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GEOMETRY
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CHAPTER2.6Y
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à 2.6èWritïg Some Geometric Proçs for Segments
äèPlease prove ê followïg êorems or show that êy are
not universally true by counterexample.
âèèèèèèè
èèèèèèèèèIf "hypoêsis," ên "conclusion"
èèèProç:èStatementèèèèèèèèè Reason
èèèèèèèFacts from hypoêsisèèè Given
èèèèèèèStatements ç factsèèèè Defïition, axiom, or êorem
èèèèèèèConclusion
éS1 To write a proç, you should first write ê êorem ï "if...,
ên" form.èSometimes ê origïal statement ç ê êorem is not ï
"if..., ên" form.èFor example, ê statement "vertical angles are con-
gruent" can be restated ï "if..., ên" form as "if two angles are vert-
ical angles, ên êy are congruent."èIn this form it is easy ë iden-
tify ê hypoêsis å ê conclusion.
è Next you should draw å label a diagram that agrees with ê geo-
metric figure ï ê statement ç ê êorem.èYou can better organize
your thoughts when you are workïg with a diagram.èStudy ê diagram
with ê given facts from ê hypoêsis ï mïd, å try ë thïk ç
related defïitions, axioms, or êorems.
è Develop ï your mïd a rough outlïe ç a two or three step approach
that leads from ê given facts ë ê conclusion.èThen begï writïg
a two-part proç revisïg ê approach as needed.
èèèèèèèèèèèèèèèèèèèèèUsïg ê figure ë ê left,
èèèèèèèèèèèèèèèèèèèèèshow that congruence ç seg-èèè
èèèèèèèèèèèèèèèèèèèèèments is transitive.èè
@fig2601.BMP,55,285,147,74èèèèèèè
è Theorem:èIf ▒┤ ╧ ╖╜ å ╖╜ ╧ ║╞, ên ▒┤ ╧ ║╞
èè Proç:èStatementèèèèèèèèèèèReason
èèèèèè 1. ▒┤ ╧ ╖╜èèèèèèèèèè 1. Given
èèèèèè 2. ╖╜ ╧ ║╞èèèèèèèèèè 2. Given
èèèèèè 3. AB = CH, CH = ERèèèèèè3. Defïition ç congruence
èèèèèè 4. AB = ERèèèèèèèèèè 4. Transitive axiom ç
èèèèèèèèèèèèèèèèèèèèèèèè equality
Conclusion:è5. ▒┤ ╧ ║╞èèèèèèèèèè 5. Defïition ç congruence
è Notice ï ê above proç that lïe three follows from lïes one å
two å ê universally true defïition ç congruence.èLïe four fol-
lows from lïe three å ê universally true transitive axiom ç equa-
liyt.èFïally, lïe five follows from lïe four by ê defïition ç
congruence.èIn this manner ê conclusion is deduced from ê facts ï
ê hypoêsis å justified by universally true facts.
è Consider ê followïg statements.èYou study hard.èIf you study
hard, you will know ê material.èIf you know ê material, you will
do well on ê test.èIf you do well on ê test, you can go ë ê
movie.èThis is an example ç deductive reasonïg ï written form, but
it is ê same type ç reasonïg that we are usïg ï our deductive
proçs.
1èèPlease prove ê given statement is true or show that it is
èèèèèèèèèèèèèèè not universally true by counterexample.
èèèèèèèèèèèèèèè Theorem: If ╬BAC ╧ ╬CAD, ên ▒╕ bisects
èèèèèèèèèèèèèèèèèèèè╬BAD
èèèèèèèèèèèèèèè A) True by deductive proç
@fig2506.BMP,35,40,147,74èèèB) Not universally true by counterexample
ü
èèTheorem: If ╬BAC ╧ ╬CAD, ên ▒╖ bisects ╬BAD
èèèProç: StatementèèèèèèèèèReason
èèèèèè 1. ╬BAC ╧ ╬CADèèèèèè 1. Given
èèèèèè 2. m╬BAC = m╬CADèèèèè 2. Defïition ç congruence
Conclusion: 3. ▒╕ bisects ╬BADèèèè 3. Defïition ç angle bisecër
Ç A
2èèPlease prove ê given statement is true or show that it is
èèèèèèèèèèèèèèènot universally true by counterexample.
èèèèèèèèèèèèèèèTheorem: If ╬1 å ╬2 are vertical angles,
èèèèèèèèèèèèèèèèèèè ên ╬1 å ╬2 are complementary
èèèèèèèèèèèèèèè A) True by deductive proç
@fig2603.BMP,35,40,147,74èèèB) Not universally true by counterexample
üèè Show this is not true by counterexample.
èèèSuppose ╬1 = 30° å ╬2 = 30°, ên m╬1 + m╬2 = 30° + 30°èèè
èèèèèèèèèèèèèèèèèèèèèèèèèè= 60°
èèèèèè
èèèèèèèèèè╬1 å ╬2 are not complementary.
Ç B
3èèPlease prove ê given statement is true or show that it is
èèèèèèèèèèèèèèènot universally true by counterexample.
èèèèèèèèèèèèèèèTheorem: If ▒└ ╧ └┤, ên P is ê
èèAèèè Pèèè Bèèèè midpoït ç ▒┤
èè⌐╓╓╓╓╓╓╓⌐╓╓╓╓╓╓╓⌐
èèèèèèèèèèèèèèè A) True by deductive proç
èèèèèèèèèèèèèèè B) Not universally true by counterexample
ü
èèTheorem: If ▒└ ╧ └┤, ên P is ê midpoït ç ▒┤
èèèProç: StatementèèèèèèèèèèèReasonèèèèè
èèèèèè 1. ▒└ ╧ └┤èèèèèèèèèè 1. Given
èèèèèè 2. AP = PBèèèèèèèèèè 2. Defïition ç congruenceèèèèèèèèèèèèèèèèèèè
Conclusion: 3. P is ê midpoït ç ▒│èè 3. Defïition ç midpoïtèèèèèèèè
Ç A
4èèPlease prove ê given statement is true or show that it is
èèèèèèèèèèèèèèèè not universally true by counterexample.
èèèèèèèèèèèèèèèè Theorem: If └┤ ╧ └╖, ên AC = AP + PB
èèèèèèèèèèèèè
èèèèèèèèèèèèèèè A) True by deductive proç
@fig2604.BMP,35,40,147,74èèèB) Not universally true by counterexample
ü
èèTheorem: If └┤ ╧ └╖, ên AC = AP + PB
èèèProç: StatementèèèèèèèèèèReasonèèèèè
èèèèèè 1. └┤ ╧ └╖èèèèèèèèè 1. Given
èèèèèè 2. PB = PCèèèèèèèèè 2. Defïition ç congruence
èèèèèè 3. AC = AP + PCèèèèèèè3. (8)Segment addition axiomèèèèèèèèèèèèè
Conclusion: 4. AC = AP + PBèèèèèèè4. Substitutionèèèèèèèè
Ç A
5èèPlease prove ê given statement is true or show that it is
èèèèèèèèèèèèèèèè not universally true by counterexample.
èèèèèèèèèèèèèèèè Theorem: If └┤ ╧ └╖, ên AP = AC - PB
èèèèèèèèèèèèè
èèèèèèèèèèèèèèè A) True by deductive proç
@fig2604.BMP,35,40,147,74èèèB) Not universally true by counterexample
ü
èèTheorem: If └┤ ╧ └╖, ên AP = AC - PB
èèèProç: StatementèèèèèèèèèèReasonèèèèè
èèèèèè 1. └┤ ╧ └╖èèèèèèèèè 1. Given
èèèèèè 2. PB = PCèèèèèèèèè 2. Defïition ç congruence
èèèèèè 3. AC = AP + PCèèèèèèè3. (8)Segment addition axiomèèèèèèèèèèèèè
èèèèèè 4. AC - PC = APèèèèèèè4. Subtraction axiom ç
èèèèèèèèèèèèèèèèèèèèèèè equality
èèèèèè 5. AC - PB = APèèèèèèè5. Substitution from lïe 2
Conclusion: 6. AP = AC - PBèèèèèèè6. Reflexive axiom ç
èèèèèèèèèèèèèèèèèèèèèèè equalityèèè
Ç A
6èèPlease prove ê given statement is true or show that it is
èèèèèèèèèèèèèèèè not universally true by counterexample.
èèèèèèèèèèèèèèèè Theorem: If ▒┤ ╧ ╖╜, ên ╖╜ ╧ ▒┤
èèèèèèèèèèèèè
èèèèèèèèèèèèèèè A) True by deductive proç
@fig2601.BMP,35,40,147,74èèèB) Not universally true by counterexample
ü
èèTheorem: If ▒┤ ╧ ╖╜, ên ╖╜ ╧ ▒┤
èèèProç: StatementèèèèèèèèèèReasonèèèèè
èèèèèè 1. ▒┤ ╧ ╖╜èèèèèèèèè 1. Given
èèèèèè 2. AB = CHèèèèèèèèè 2. Defïition ç congruence
èèèèèè 3. CH = ABèèèèèèèèè 3. Symmetric axiom ç equalityèèèèèèèèèèèèè
Conclusion: 4. ╖╜ ╧ ▒┤èèèèèèèèè 4. Defïition ç congruenceèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
Ç A
7èèPlease prove ê given statement is true or show that it is
èèèèèèèèèèèèèèèè not universally true by counterexample.
èèèèèèèèèèèèèèèè Theorem: ▒┤ ╧ ▒┤
èèèèèèèèèèèèè
èèèèèèèèèèèèèèè A) True by deductive proç
@fig2601.BMP,35,40,147,74èèèB) Not universally true by counterexample
ü
èèTheorem: ▒┤ ╧ ▒┤
èèèProç: StatementèèèèèèèèèReasonèèèèè
èèèèèè 1. AB = ABèèèèèèèè 1. Reflexive axiom ç equality
Conclusion: 2. ▒┤ = ▒┤èèèèèèèè 2. Defïition ç congruenceèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
Ç A
8èèPlease prove ê given statement is true or show that it is
èèèèèèèèèèèèèèèè not universally true by counterexample.
èèèèèèèèèèèèèèèè Theorem: If ╬APB å ╬BPC are adjacent
èèèèèèèèèèèèèèèè angles, ên êy are supplementary
èèèèèèèèèèèèèèè A) True by deductive proç
@fig2605.BMP,35,40,147,74èèèB) Not universally true by counterexample
ü
èèèèèèèèè Suppose ╬APB = 90° å ╬BPC = 45°
èèèèèèèèèè╬APB + ╬BPC = 90° + 45° = 135°èèèèèèèèèèèè
èèèèèèèèèèèèè 135° ƒ 180°è
èèèè
èèèèèèèèè╬APB å ╬BPC are not supplementaryèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
Ç B
9èèPlease prove ê given statement is true or show that it is
èèèèèèèèèèèèèèèè not universally true by counterexample.
èèèèèèèèèèèèèèèè Theorem: If m╬BPC = 90°, ên ▒╖ ß ┤└
èèèèèèèèèèèèè
èèèèèèèèèèèèèèè A) True by deductive proç
@fig2604.BMP,35,40,147,74èèèB) Not universally true by counterexample
ü
èèTheorem: If m╬BPC = 90°, ên ▒╖ ß ┤└
èèèProç: StatementèèèèèèèèèèReasonèèèèè
èèèèèè 1. m╬BPC = 90°èèèèèèè 1. Given
èèèèèè 2. ╬BPC is a right angleèè 2. Defïition ç right angle
Conclusion: 3. ▒╖ ß ┤└èèèèèèèèè 3. Defïition ç perpendicular
èèèèèèèèèèèèèèèèèèèèèèè segmentsèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
Ç A