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CHAPTER7.1Y
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à 7.1èDefïitions for Circles å Spheres
äèPlease answer ê followïg questions about circles
å spheres.
â
èè Two circles are congruent if å only if êir radii are equal.è
éS1
Defïition 7.1.1èCIRCLE:èA circle is ê set ç all poïts ï a plane
that are a fixed distance from a poït called ê center ç ê circle.
Defïition 7.1.2èRADIUS:èA radius ç a circle is a lïe segment
joïïg ê center ç ê circle ë one ç ê poïts on ê circle.
Defïition 7.1.3èDIAMETER:èA diameter ç a circle is a lïe segment
that contaïs ê center ç ê circle å has its endpoïts on ê
circle.
èèèèèèèèèèèèèèèèèèè In this figure, ê circle has
èèèèèèèèèèèèèèèèèèè center P, └╖ is a radius, åèè
èèèèèèèèèèèèèèèèèèè ▒┤ is a diameter.è╣╛ is a
èèèèèèèèèèèèèèèèèèè secant, ┼═ is a tangent, å
èèèèèèèèèèèèèèèèèèè ║╜ is a chord.èThe circle with
@fig7101.BMP,65,210,147,74èèèèèè center P is called circle P.
Theorem 7.1.1èThe diameter, AB, ç circle P is twice ê radius.
Proç: Statementèèèèèèèèèèè Reason
èèè 1. ▒┤ is a diameterèèèèèè 1. Given ï ê figureèè
èèè 2. AB = AP + PBèèèèèèèè 2. (8)Segment addition axiom
èèè 3. ▒└, └┤ are radiièèèèèè 3. Defïition ç radius
èèè 4. AB = r + rèèèèèèèèè 4. Substitution
èèè 5. AB = 2rèèèèèèèèèèè5. Distributive axiom
Defïition 7.1.4èSECANT:èA secant is a lïe that ïtersects a circle
ï two poïts.
Defïition 7.1.5èTANGENT:èA tangent ë a circle is a lïe that ïter-
sects ê circle ï exactly one poït.èThis poït is called ê poït
ç tangency.
Defïition 7.1.6èCHORD:èA chord is a lïe segment with endpoïts on
a circle.
Axiom 21:èTwo circles are congruent if å only if êir radii are
equal.
è A sphere is ê set ç all poïts ï space that are a fixed distance
from a poït called ê center ç ê sphere.èA radius ç a sphere is
a lïe segment joïïg ê center ç ê sphere ë a poït on ê
sphere.èA diameter ç a sphere is a lïe segment that contaïs ê cen-
ter å has its endpoïts on ê sphere.
è The ïtersection ç a plane that passes through ê center ç aè
sphere is called a great circle.èThe ïtersection ç a plane that
does not contaï ê center ç a sphere is a small circle.èA tangent ë
a sphere is a lïe or a plane that ïtersects ê sphere ï exactly one
poït.
1
èèèèèèèèèèèèèèèèèè Name a diameter ç circle P.
èèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèA) ╣╛èèè B) ▒┤èèè C) └╖
@fig7101.BMP,35,40,147,74
ü
èèèèèèèèèèè ▒┤ is a diameter ç circle P.
Ç B
2
èèèèèèèèèèèèèèèèèèèName a secant ç circle P.
èèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèA) ╣╛èèè B) ▒┤èèè C) └╖
@fig7101.BMP,35,40,147,74
ü
èèèèèèèèèèè ╣╛ is a secant ç circle P.
Ç A
3
èèèèèèèèèèèèèèèèèèèName a radius ç circle P.
èèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèA) ╣╛èèè B) ▒┤èèè C) └╖
@fig7101.BMP,35,40,147,74
ü
èèèèèèèèèèè └╖ is a radius ç circle P.
Ç C
4
èèèèèèèèèèèèèèèèèèèName a tangent ç circle P.
èèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèè A) Rèèè B) ║╜èèè C) ┼═
@fig7101.BMP,35,40,147,74
ü
èèèèèèèèèèè ┼═ is a tangent ç circle P.
Ç C
5
èèèèèèèèèèèèèèèèèèè Name a chord ç circle P.
èèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèè A) Rèèè B) ║╜èèè C) ┼═
@fig7101.BMP,35,40,147,74
ü
èèèèèèèèèèèè║╜ is a chord ç circle P.
Ç B
6
èèèèèèèèèèèèèèèèèName a poït ç tangency ç circle P.
èèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèèA) Tèèè B) ║╜èèè C) R
@fig7101.BMP,35,40,147,74
ü
èèèèèèèèèèèè T is a poït ç tangency.
Ç A
7
èèèèèèèèèèèèèèèèèè If PC = 6, fïd AB ï circle P.
èèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèèA) 24èèè B) 10èèè C) 12
@fig7101.BMP,35,40,147,74
ü
èèèèèèèèèèèèèAB = 2·PC = 2·6 = 12
Ç C
8
èèèèèèèèèèèèèèèèèè If AB = 24, fïd PC ï circle P.
èèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèèèèA) 24èèè B) 10èèè C) 12
@fig7101.BMP,35,40,147,74
ü
èèèèèèèèèèèè PC = 1/2AB = 1/2(24) = 12
Ç C
9
èèèèèèèèèèèèèèèèèèèèèè Name ║┤.
èèèèèèèèèèèèèèè
èèèèèèèèèèèèèèèèA) Chordèè B) Secantèè C) Tangent
@fig7101.BMP,35,40,147,74
ü
Although this lïe segment is not drawn on ê figure, we can still
talk about it å describe it as though it where êre.
èèèèèèèèèèèèèèè║┤ is a chord.
Ç A
10
èèèèèèèèèèèèèèèèèèèèèèè Name ░╡.
èèèèèèèèèèèèèèè
èèèèèèèèèèèèèèè A) Diameterèè B) Secantèè C) Tangent
@fig7101.BMP,35,40,147,74
ü
Once agaï this lïe is not drawn on ê figure, but we can still de-
scribe it as though it where êre.
èèèèèèèèèèèèèèè ░╡ is a secant.
Ç B
11
èèèèèèèèèèè All secants are also chords.èè
èèèèèèèèè
èèèèèèèèèèèèèèè
èèèèèèèèèèèè A) TrueèèèèB) False
ü
èèèFalse.èA secant is a lïe, whereas a chord is a lïe segment.
Ç B
12
èèèèèèèèèèèèAll secants contaï chords.èè
èèèèèèèèè
èèèèèèèèèèèèèèè
èèèèèèèèèèèèèA) TrueèèèèB) False
ü
èèèèèèèèèèèèèèèèè Trueèè
Ç A
13
èèèèèèèè A diameter ç a great circle ç a sphereèè
èèèèèèèè is equal ë ê diameter ç ê sphere.èè
èèèèèèèèèèèèèèè
èèèèèèèèèèèèèA) TrueèèèèB) False
ü
èèèèèèèèèèèèèèèèè Trueèè
Ç A
14
èèèèèè The longest chords ç a circle are also diameters.èè
èèèèè
èèèèèèèèèèèèèèè
èèèèèèèèèèèèèA) TrueèèèèB) False
ü
èèèèèèèèèèèèèèèèè Trueèè
Ç A
15
èèèèèèèTangents ç circles contaï at least one chord.èèè
èèèèè
èèèèèèèèèèèèèèè
èèèèèèèèèèèèèA) TrueèèèèB) False
ü
èèèFalse.èTangents ç circles ïtersect ê circle ï exactly
èèèone poït, whereas chords ïtersect ê circle ï two poïts.èèèè
Ç B
16
èèèèèèèèAll secants contaï diameters ç a circle.èèè
èèèèè
èèèèèèèèèèèèèèè
èèèèèèèèèèèèèA) TrueèèèèB) False
ü
èFalse.èOnly secants that pass through ê center contaï diameters.èèèèèè
Ç B
17
èèèèèèè Some chords can also be a radius ç a circle.èèè
èèèèè
èèèèèèèèèèèèèèè
èèèèèèèèèèèèèA) TrueèèèèB) False
ü
èèèèFalse.èA chord has its endpoïts on ê circle, whereasè
èèèèa radius has one endpoït at ê center ç ê circle.èèèèè
Ç B
18
èè In a sphere, ê diameters ç two small circles can be congruent.è
èèèèè
èèèèèèèèèèèèèèè
èèèèèèèèèèèèèA) TrueèèèèB) False
ü
èèèèèTrue.èThere are an unlimited number ç small circlesèè
èèèèèç a sphere that have diameters ê same length.èèè
Ç A