THINK AND DISCUSS
1. Which step in a proof should match the Prove statement?
2. Why is it important to include every logical step in a proof?
3. List four things you can use to justify a step in a proof.
4. GET ORGANIZED Copy and complete the graphic organizer.
In each box, describe the steps of the proof process.
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2-6
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Exercises
KEYWORD: MG7 2-6
KEYWORD: MG7 Parent
GUIDED PRACTICE
Vocabulary Apply the vocabulary from this lesson to answer each question.
1. In a two-column proof, you list the ? in the left column and the ? in
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the right column. (statements or reasons)
2. A
SEE EXAMPLE
1
p. 110
SEE EXAMPLE
? is a statement you can prove. (postulate or theorem)
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3. Write a justification for each step, given that m∠A = 60° and m∠B = 2m∠A.
1.
2.
3.
4.
5.
6.
2
p. 111
m∠A = 60°, m∠B = 2m∠A
m∠B = 2(60°)
m∠B = 120°
m∠A + m∠ B = 60° + 120°
m∠A + m∠B = 180°
∠A and ∠B are supplementary.
Given: ∠2 ≅ ∠3
Prove: ∠1 and ∠3 are supplementary.
Proof:
1. Given
2. m∠2 = m∠3
2. a.
?
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4. m∠1 + m∠2 = 180°
5. m∠1 + m∠3 = 180°
6. d.
3
?
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Reasons
1. ∠2 ≅ ∠3
3. b.
p. 112
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4. Fill in the blanks to complete the two-column proof.
Statements
SEE EXAMPLE
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?
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3. Lin. Pair Thm.
4. Def. of supp. 
5. c.
?
Steps 2, 4
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6. Def. of supp. 
5. Use the given plan to write a two-column proof.
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Given: X is the midpoint of AY, and Y is the midpoint of XB.
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Prove: AX ≅ YB
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Plan: By the definition of midpoint, AX ≅ XY, and XY ≅ YB.
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Use the Transitive Property to conclude that AX ≅ YB.
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2- 6 Geometric Proof
113