Proof: Cosine 3

Let's prove the following theorem:

Proof:

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) (Cosine 2)
2	(distance BA) / (distance CA) = (distance AB) / (distance AC)	(distance BA) / (distance CA) = (distance AB) / (distance AC) (divide_distances)
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) (Transitive Property of Equality)

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