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CHAPTER1.3Y
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à 1.3èAxioms for Poïts, Lïes, å Planes
äèPlease answer ê followïg questions about axioms for
poïts, lïes, å planes.
â
èèè Axioms are true statements ï a maêmatical system, butè
èèè it is not possible ë prove that êy are true.èTheoremsèè
èèè are true statements that can be proven.
éS In ê last section it was mentioned that all maêmatical sys-
tems are developed ê same way.èThe first step is ë identify ê un-
defïed terms, ê second step is ë state some defïitions, ê third
step is ë state axioms usually usïg one or more undefïed terms, ên
êorems are developed by referrïg ë ê axioms, defïitions, å
undefïed terms.è
è The example that we used ï ê last section ë illustrate this idea
was algebra.èThe undefïed terms for algebra are set å element.èAn
example ç a defïition is "two sets are equal if å only if êy have
ê same elements."è
è The next step is ë state an axiom.èOne axiom for algebra is called
ê commutative axiom for addition.èThis states that you can add two
numbers ëgeêr ï a different order å get ê same answer.èFor ex-
ample, 2+5 å 5+2 both give you an answer ç 7.èThis is not very sur-
prisïg, but that is ê way axioms are.èThey are true statements
about very simple facts that are so basic å fundamental that it is not
possible ë prove that êy are true.
è In geometry ê undefïed terms are poït, lïe, å plane.èIn ê
last section we looked at eleven defïitions about poïts, lïes, å
planes.èIn this section we will identify five axioms about poïts,
lïes, å planes.èRemember axioms are statements about very simple
facts that are so basic that êy can not be proven.èWe will, however,
assume that êy are true å use êm as facts ë prove oêr facts.
èèThis is ê way Euclid developed geometry.èHe wanted ë keep ê
list ç undefïed terms as small as possible so he narrowed it down ë
just poït, lïe, å plane.èHe also wanted ë keep ê list ç axioms
small.èHe felt it is better ë be able ë prove as many facts as poss-
ible.è
èèUndefïed terms, defïitions, å axioms all have ë be assumed.
Oêr facts that can be proven are called êorems.èWe will have aè
ëtal ç twenty-five axioms.èThe first five are given as follows:
Axiom 1:èSpace contaïs at least four noncoplanar, noncollïear poïts.
A plane contaïs at least three noncollïar poïts.èA lïe contaïs at
least two poïts.
Axiom 2:èIf two poïts are contaïed ï a plane, ên ê lïe that
contaïs êm is also contaïed ï ê plane.
Axiom 3:èIf two planes ïtersect, êy ïtersect ï a lïe.
Axiom 4:èTwo distïct poïts determïe a lïe.
Axiom 5:èThree noncollïear poïts determïe a plane.
1
èèèèèè How many lïes can pass through two poïts?
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèèèèA)èThreeèèB)èTwoèè C)èOneèè D)èNoneè
ü
èèèèèèOne lïe can pass through two distïct poïts.
Ç C
2
èHow many planes are determïed by three distïct noncollïear poïts?
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèèèèA)èOneèè B)èTwoèè C)èThreeèè D)èNoneè
ü
èèèOne plane is determïed by three distïct noncollïear poïts.
Ç A
3
è How many lïes can two distïct planes have as êir ïtersection?
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèè A)èTwoèè B)èOne or Zeroèè C)èThreeèè D)èNoneè
ü
èTwo planes can have one lïe ç ïtersection or no lïes if êy are
parallel.
Ç B
4
èIf two poïts from a lïe are contaïed ï a plane, how many oêr
poïts from ê lïe are ï ê plane?
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèèèèA)èTwoèèèB)èOneèèèC)èAllèèèD)èNoneè
ü
èèèèèAll poïts from ê lïe are contaïed ï ê plane.
Ç C
5
è Space contaïs at least _________ noncoplanar, noncollïear poïts.
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèèè A)èFourèèèB)èThreeèèèC)èTwoèèèD)èNoneè
ü
èè Space contaïs at least four noncoplanar, noncollïear poïts.
Ç A
6
èèè A plane contaïs at least _________ noncollïear poïts.
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèèèA)èThreeèèè B)èTwoèèè C)èOneèèèD)èNoneè
ü
èèèèèA plane contaïs at least three noncollïear poïts.
Ç A
7
èèèèèèèA lïe contaïs at least _________ poïts.
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèèèA)èThreeèèè B)èTwoèèè C)èOneèèèD)èNoneè
ü
èèèèèè A lïe contaïs at least two distïct poïts.
Ç B
8
èèèèèèè Two poïts completely determïe aè_________.
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèè A)èSpaceèèè B)èPlaneèèè C)èLïeèèèD)èPoïtè
ü
èèèèèèèèTwo poïts completely determïe a lïe.
Ç C
9
èèèèèè Three noncollïear poïts determïe aè_________.
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèè A)èSpaceèèè B)èPlaneèèè C)èLïeèèèD)èPoïtè
ü
èèèèèèè Three noncollïear poïts determïe a plane.
Ç B
10
èè_________ contaïs at least four noncollïear, noncoplanar poïts.
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèè A)èSpaceèèè B)èPlaneèèè C)èLïeèèèD)èPoïtè
ü
èèèSpace contaïs at least four noncollïear, noncoplanar poïts.
Ç A
11
èIf two distïct poïts lie ï a plane, ên ê ________ that contaïs
ê poïts is also contaïed ï ê plane.
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèèè
èèèè A)èSpaceèèè B)èPlaneèèè C)èLïeèèèD)èPoïtè
ü
èèèèèèèèèèèèèèèèèLïe
Ç C