Proof: Collinear Then Equal 2

Let's prove the following theorem:

if m∠DAX = m∠XBC and m∠AXB = 180, then m∠DAB = m∠ABC

A B X D C

Proof:

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

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