2. Two geometric figures with
exactly the same size and
shape.
The Idea of a CongruenceThe Idea of a Congruence
A C
B
DE
F
3. How much do youHow much do you
need to know. . .need to know. . .
. . . about two triangles
to prove that they
are congruent?
4. In Lesson 4.2, you learned that if all
six pairs of corresponding parts (sides
and angles) are congruent, then the
triangles are congruent.
Corresponding PartsCorresponding Parts
∆ABC ≅ ∆
DEF
B
A
C
E
D
F
1. AB ≅ DE
2. BC ≅ EF
3. AC ≅ DF
4. ∠ A ≅ ∠ D
5. ∠ B ≅ ∠ E
6. ∠ C ≅ ∠ F
5. Do you needDo you need all six ?all six ?
NO !
SSS
SAS
ASA
AAS
22. Let’s PracticeLet’s Practice
Indicate the additional information needed
to enable us to apply the specified
congruence postulate.
For ASA:
For SAS:
∠B ≅ ∠D
For AAS: ∠A ≅ ∠F
AC ≅ FE
23. HWHW
Indicate the additional information needed
to enable us to apply the specified
congruence postulate.
For ASA:
For SAS:
For AAS:
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