Proof: Collinear Then Equal

Let's prove the following theorem:

if m∠DAB = m∠CBA and m∠AXB = 180, then m∠DAX = m∠CBX

A B X D C

Proof:

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Given
1 m∠DAB = m∠CBA
2 m∠AXB = 180
Proof Table
# Claim Reason
1 m∠DAB = m∠DAX if m∠AXB = 180, then m∠DAB = m∠DAX
2 m∠DAX = m∠CBA if m∠DAB = m∠DAX and m∠DAB = m∠CBA, then m∠DAX = m∠CBA
3 m∠CBA = m∠CBX if m∠AXB = 180, then m∠CBA = m∠CBX
4 m∠DAX = m∠CBX if m∠DAX = m∠CBA and m∠CBA = m∠CBX, then m∠DAX = m∠CBX

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