Proving Triangles Congruent

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Proving Triangles Congruent
Free powerpoints at http//www.worldofteaching.com
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The Idea of a Congruence
Two geometric figures with exactly the same
size and shape.
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How much do you need to know. . .
. . . about two triangles to
prove that they are congruent?
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Corresponding Parts
In Lesson 4.2, you learned that if all six pairs
of corresponding parts (sides and angles) are
congruent, then the triangles are congruent.
?ABC ? ? DEF
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Do you need all six ?
NO !
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Side-Side-Side (SSS)
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Side-Angle-Side (SAS)


B

E






F
A



C
D

1. AB ? DE
2. ?A ? ? D
3. AC ? DF

?ABC ? ? DEF
included angle
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Included Angle
The angle between two sides
? H
? G
? I
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Included Angle
Name the included angle YE and ES ES and
YS YS and YE
? E
? S
? Y
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Angle-Side-Angle (ASA)


B

E






F
A



C
D

1. ?A ? ? D
2. AB ? DE
3. ? B ? ? E

?ABC ? ? DEF
included side
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Included Side
The side between two angles
GI
GH
HI
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Included Side
Name the included angle ?Y and ?E ?E and
?S ?S and ?Y
YE
ES
SY
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Angle-Angle-Side (AAS)


B

E






F
A



C
D

1. ?A ? ? D
2. ? B ? ? E
3. BC ? EF

?ABC ? ? DEF
Non-included side
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Warning No SSA Postulate
There is no such thing as an SSA postulate!
E
B
F
A
C
D
NOT CONGRUENT
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Warning No AAA Postulate
There is no such thing as an AAA postulate!
E
B
A
C
F
D
NOT CONGRUENT
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The Congruence Postulates
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Name That Postulate
(when possible)
SAS
ASA
SSA
SSS
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Name That Postulate
(when possible)
AAA
ASA
SSA
SAS
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Name That Postulate
(when possible)
Vertical Angles
Reflexive Property
SAS
SAS
Reflexive Property
Vertical Angles
SSA
SAS
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HW Name That Postulate
(when possible)
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HW Name That Postulate
(when possible)
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Lets Practice
Indicate the additional information needed to
enable us to apply the specified congruence
postulate.
For ASA
?B ? ?D
For SAS
?A ? ?F
For AAS
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HW
Indicate the additional information needed to
enable us to apply the specified congruence
postulate.
For ASA
For SAS
For AAS