Proof: Right Angle Reverse

Let's prove the following theorem:

if ∠ABC is a right angle, then ∠CBA is a right angle

A B C

Proof:

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Given
1 ABC is a right angle
Proof Table
# Claim Reason
1 m∠ABC = 90 if ∠ABC is a right angle, then m∠ABC = 90
2 m∠ABC = m∠CBA m∠ABC = m∠CBA
3 m∠CBA = 90 if m∠ABC = m∠CBA and m∠ABC = 90, then m∠CBA = 90
4 CBA is a right angle if m∠CBA = 90, then ∠CBA is a right angle
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