Proof: Cosine 3

Let's prove the following theorem:

if ∠ABC is a right angle, then cosine of (m∠CAB) = (distance AB) / (distance AC)

Proof:

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Given
1 ∠ABC is a right angle
Proof Table
# Claim Reason
1 cosine of (m∠CAB) = (distance BA) / (distance CA) if ∠ABC is a right angle, then cosine of (m∠CAB) = (distance BA) / (distance CA)
2 (distance BA) / (distance CA) = (distance AB) / (distance AC) (distance BA) / (distance CA) = (distance AB) / (distance AC)
3 cosine of (m∠CAB) = (distance AB) / (distance AC) if cosine of (m∠CAB) = (distance BA) / (distance CA) and (distance BA) / (distance CA) = (distance AB) / (distance AC), then cosine of (m∠CAB) = (distance AB) / (distance AC)

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