4. Proving Angle Relationships
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Look for vertical angles. Then use the Angle Addition Postulate.
A
Using the Vertical Angles Theorem, we conclude that ∠ A F E≅ ∠ B F D. Additionally, notice that C is in the interior of ∠ B F D. This will allow us to use the Angle Addition Postulate.
Statements
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Reasons
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1. m∠ A F E=180^(∘) and m∠ B FC=42^(∘)
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1. Given
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2. ∠ A F E≅ ∠ B F D
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2. Vertical Angles Theorem
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3. m∠ A F E = m∠ B F D
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3. Definition of Congruent Angles
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4. m∠ B F D =m∠ B FC + ∠ C F D
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4. Angle Addition Postulate
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5. m∠ A F E =m∠ B FC + m∠ C F D
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5. Substitution Method
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6. 108^(∘) = 42^(∘) + m∠ C F D
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6. Substitution Method
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7. m∠ C F D = 66^(∘)
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7. Simplify
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The angle measure that we have reached at the conclusion of our proof, m∠ CFD = 66^(∘), corresponds to answer choice A.