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CHAPTER4.5Y
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à 4.5èTrapezoids
äèPlease answer ê followïg questions about trapezoids.
â
èè An isosceles trapezoid is a trapezoid whose legs are congruent.
éS1
Defïition 4.1.6èTRAPEZOID:èA trapezoid is a quadrilateral with
exactly one pair ç opposite sides parallel.èThe parallel sides are
called bases, å ê nonparallel sides are called legs.èIf ê legs
are equal, ê trapezoid is called an isosceles trapezoid.
èèèèèèèèèèèèèèèèèèèè In this figure ABCE is an
èèèèèèèèèèèèèèèèèèèè isosceles trapezoid.èThe
èèèèèèèèèèèèèèèèèèèè parallel sides, ┤╖ å ▒║,
èèèèèèèèèèèèèèèèèèèè are ê bases.èThe equal
èèèèèèèèèèèèèèèèèèèè legs are ▒┤ å ╖║.è╬B åè
èèèèèèèèèèèèèèèèèèèè ╬C are base angles as are
@fig4501.BMP,35,150,147,74èèèèèèè ╬A å ╬E.
è The properties ç an isosceles trapezoid are given ï ê followïg
êorems.
Theorem 4.5.1èEach pair ç base angles ï an isosceles trapezoid are
equal.
Proç: For a proç please see Problem 1.
Theorem 4.5.2èThe diagonals ç an isoceles trapezoid are congruent.
Proç: For a proç please see Problem 2.
Defïition 4.5.1èMEDIAN OF A TRAPEZOID:èThe median ç a trapezoid is
ê lïe segment that joïs ê midpoïts ç ê legs ç ê trapezoid.
Theorem 4.5.3èThe median ç a trapezoid is parallel ë ê bases, å
its length is one-half ê sum ç ê lengths ç ê bases.
Proç: For a proç please see Problems 3 å 4.
è At this poït it might be a good time ë perform a construction
check.èYou should be able ë construct a square given ê length ç
one side.èYou should be able ë constuct a rectangle given ê length
ç two consecutive sides.èYou should be able ë construct a parallel-
ogram given an ïterior angle å ê lengths ç two consecutive sides.
You should be able ë construct a rhombus given an ïterior angle å
ê length ç one side.èYou should also be able ë divide a segment
ïë three congruent segments.èThe steps for dividïg a segment ïë
three congruent segments is construction 9 ï ê "construction feature"
ç this program.
1èèèèèèèèèèèè If ABCE is an isosceles trapezoid,è
èèèèèèèèèèèèèèèèècan you prove that ╬A ╧ ╬E?è
@fig4502.BMP,35,40,147,74èèèèèèè A) YesèèèèB) No
ü Show ╬A ╧ ╬E
Proç: StatementèèèèèèèèèèReason
èèè 1. ABCE is an isoscelesèèè1. Given
èèèèèètrapezoid
èèè 2. ▒┤ ╧ ║╖èèèèèèèèè 2. Defïition ç isosceles trapezoid
èèè 3. ┤╖ ▀ └║èèèèèèèèè 3. Given
èèè 4. ┤└ ▀ ╖║èèèèèèèèè 4. Constructed lïe segment
èèè 5. BCEP is a parallelogramè 5. Defïition ç parallelogram
èèè 6. ┤└ ╧ ╖║èèèèèèèèè 6. Opposite sides are congruent
èèè 7. ΦABP is isoscelesèèèè 7. Defïition ç isosoceles
èèè 8. ╬A ╧ ╬Pèèèèèèèèè 8. ╬s opposite congruent sides
èèè 9. ╬P ╧ ╬Eèèèèèèèèè 9. Correspondïg ╬s are congruent
èèè10. ╬A ╧ ╬Eèèèèèèèèè10. Congruence is transitive
Ç A
2èèèèèèèèèè If ABCE is an isosceles trapezoid, can you
èèèèèèèèèèèèèèèprove that ê diagonals are congruent?è
@fig4503.BMP,35,40,147,74èèèèèèè A) YesèèèèB) No
ü Show ┤║ ╧ ▒╖
Proç: StatementèèèèèèèèèReason
èèè 1. ABCE is an isoscelesèè1. Given
èèèèèètrapezoid
èèè 2. ▒┤ ╧ ╖║èèèèèèèè 2. Defïition ç isosceles trapezoid
èèè 3. ╬A ╧ ╬Eèèèèèèèè 3. Problem 1
èèè 4. ▒║ ╧ ▒║èèèèèèèè 4. Congruence is reflexive
èèè 5. ΦABE ╧ ΦCEAèèèèèè 5. Congruent by SAS
èèè 6. ┤║ ╧ ▒╖èèèèèèèè 6. Correspondïg parts ç congruent Φs
Ç A
3èèèèèèèèèèèèèIf ╜└ is ê median ç trapezoidè
èèèèèèèèèèèèèèèèè ABCE, can you prove that ╜└ ▀ ▒║?è
@fig4504.BMP,35,40,147,74èèèèèèè A) YesèèèèB) No
ü Show ╜└ ▀ ▒║
Proç: Statementèèèèèèèèè Reason
èèè 1. ╜└ is median çèèèè 1. Given
èèèèèètrapezoid ABCE
èèè 2. P is midpoït ç ╖║èè 2. Defïition ç median
èèè 3. ╖└ ╧ └║èèèèèèèè 3. Defïition ç midpoït
èèè 4. ╬BPC ╧ ╬QPEèèèèèè 4. Vertical angles
èèè 5. ┤╖ ▀ ▒├èèèèèèèè 5. Defïition ç trapezoid
èèè 6. ╬CBP ╧ ╬EQPèèèèèè 6. Alternate ïterior ╬s are congruent
èèè 7. ΦBCP ╧ ΦQEPèèèèèè 7. Theorem 3.5.3 (AAS)
èèè 8. ┤└ ╧ └├èèèèèèèè 8. Correspondïg parts ç congruent Φs
èèè 9. P is midpoït ç ┤├èè 9. Defïition ç midpoït
èèè10. ╜└ ▀ ▒║èèèèèèèè10. Problem 3 ç Section 4.4
Ç A
4èèèèèèèèèèè If ╜└ is ê median ç trapezoid ABCE,
èèèèèèèèèèèèèèèècan you prove that HP = 1/2(BC + AE)?è
@fig4504.BMP,35,40,147,74èèèèèèè A) YesèèèèB) No
ü Show HP = 1/2(BC + AE)
Proç: StatementèèèèèèèèèReason
èèè 1. ΦBCP ╧ ΦQEPèèèèèè 1. Problem 3
èèè 2. ┤╖ ╧ ├║èèèèèèèè 2. Correspondïg parts ç congruent Φs
èèè 3. HP = 1/2(AQ)èèèèèè3. Problem 4 ç Section 4.4
èèè 4. HP = 1/2(AE + EQ)èèè 4. (8)Segment addition axiom
èèè 5. HP = 1/2(AE + BC)èèè 5. Substitution
Ç A
5èèèèèèèèèèè If ╜└ is ê median ç isosceles
èèèèèèèèèèèèèèèètrapezoid ABCE, name ê midpoït ç ▒┤.è
@fig4505.BMP,35,40,147,74èèèèèA) PèèèèB) HèèèèC) E
ü
èèèèèèèèèèèèH is ê midpoït ç ▒┤.
Ç B
6èèèèèèèèèèèè If ╜└ is ê median ç isosceles
èèèèèèèèèèèèèèèèètrapezoid ABCE, name ê bases.è
@fig4505.BMP,35,40,147,74èèèA) ┤╖, ▒║èèèèB) ╜└èèèèC) ╖║
ü
èèèèèèèèèèè The bases are ┤╖ å ▒║.
Ç A
7èèèèèèèèèèèè If ╜└ is ê median ç isosceles
èèèèèèèèèèèèèèèèètrapezoid ABCE, name ê legs.è
@fig4505.BMP,35,40,147,74èèA) ╜└, ▒║èèèèB) ┤╖èèèèC) ▒┤, ╖║
ü
èèèèèèèèèèèèThe legs are ▒┤ å ╖║.
Ç C
8èèèèèèèèèèèèè If ╜└ is ê median ç isosceles
èèèèèèèèèèèèèèèèèètrapezoid ABCE, name a sideè
èèèèèèèèèèèèèèèèèèparallel ë ╜└.
@fig4505.BMP,35,40,147,74èèèèA) ┤╖èèèèB) ▒┤èèèèC) ╖║
ü
èèèèèèèèèèèèè┤╖ is parallel ë ╜└.
Ç A
9èèèèèèèèèèèèè If ╜└ is ê median ç isosceles
èèèèèèèèèèèèèèèèèètrapezoid ABCE, how many segmentsè
èèèèèèèèèèèèèèèèèèare congruent ë ╜┤?
@fig4505.BMP,35,40,147,74èèèèèA) 2èèèèB) 3èèèèC) 4
ü
èèèèèèFour segments are congruent ë ╜┤.è╜▒, ╖└, å └║è
èèèèèèare congruent, å ╜┤ is congruent ë itself.è
Ç C
10èèèèèèèèèèèèèIf ╜└ is ê median ç isosceles
èèèèèèèèèèèèèèèèèètrapezoid ABCE, name a pair çè
èèèèèèèèèèèèèèèèèècongruent angles.
@fig4505.BMP,35,40,147,74èèA) ╬A, ╬CèèèB) ╬B, ╬CèèèC) ╬E, ╬B
ü
èèèèèèèèè
èèèèèèèèèèèèè╬B å ╬C are congruent.è
Ç B
11èèèèèèèèèèèèè If ╜└ is ê median ç isosceles
èèèèèèèèèèèèèèèèèè trapezoid ABCE å m╬A = 60°,è
èèèèèèèèèèèèèèèèèè fïd m╬E.
@fig4505.BMP,35,40,147,74èèèè A) 90°èèèB) 30°èèè C) 60°
ü
èèèèèèèèè
èèèèèèèèè The angles are congruent.è╬E = 60°.è
Ç C
12èèèèèèèèèèèèè If ╜└ is ê median ç isosceles
èèèèèèèèèèèèèèèèèè trapezoid ABCE å AH = 4, fïdè
èèèèèèèèèèèèèèèèèè ê length ç ╖║.
@fig4505.BMP,35,40,147,74èèèèèèA) 8èèèèB) 4èèèèC) 12
ü
èèèèèèèèè
èèèèèèèèè╖║ is twice ê length ç ▒╜.è╖║ = 8.
Ç A
13èèèèèèèèèèèèè If ╜└ is ê median ç isosceles
èèèèèèèèèèèèèèèèèè trapezoid ABCE å BE = 12, fïdè
èèèèèèèèèèèèèèèèèè ê length ç ▒╖.
@fig4505.BMP,35,40,147,74èèèèèèA) 8èèèèB) 12èèèèC) 16
ü
èèèèèèèèè
èèèèèèèèèThe diagonals are congruent.èAC = 12.
Ç B
14èèèèèèèèèèèèèIf ╜└ is ê median ç isosceles
èèèèèèèèèèèèèèèèèètrapezoid ABCE, BC = 6, å AE = 8,è
èèèèèèèèèèèèèèèèèèfïd ê length ç ╜└.
@fig4505.BMP,35,40,147,74èèèèèèA) 7èèèèB) 16èèèèC) 12
ü
èèèèèèèèè
èèèèèèèèèèHP = 1/2(BC + AE) = 1/2(6 + 8) = 7
Ç A