4. Proving Triangles Congruent-ASA, AAS
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Statements
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Reasons
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1. ∠2 ≅ ∠1 and ∠1 ≅ ∠3
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1. Given
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2. ∠2 ≅ ∠3
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2. Transitive Property of Congruence
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3. ∠2 and ∠3 are alternate interior angles
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3. From the diagram
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4. AB ∥ DE
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4. Converse of Alternate Interior Angles Theorem
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From the given diagram, we can see that BD is a transversal of AB and DE. This implies that ∠2 and ∠3 are alternate interior angles.
Since ∠2 ≅ ∠1 and ∠1 ≅ ∠3, by the Transitive Property of Congruence we get ∠2 ≅ ∠3. Next, by the Converse of Alternate Interior Angles Theorem we conclude that AB ∥ DE. We summarize this proof in the following table.
Statements
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Reasons
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1. ∠2 ≅ ∠1 and ∠1 ≅ ∠3
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1. Given
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2. ∠2 ≅ ∠3
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2. Transitive Property of Congruence
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3. ∠2 and ∠3 are alternate interior angles
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3. From the diagram
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4. AB ∥ DE
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4. Converse of Alternate Interior Angles Theorem
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