Proof: Cosine 2

Let's prove the following theorem:

Proof:

Proof Table

#	Claim	Reason
1	cosine of (m∠BAC) = (distance BA) / (distance CA)	if ∠ABC is a right angle, then cosine of (m∠BAC) = (distance BA) / (distance CA) (cosine)
2	m∠BAC = m∠CAB	m∠BAC = m∠CAB (Angle Symmetry Property)
3	cosine of (m∠BAC) = cosine of (m∠CAB)	if m∠BAC = m∠CAB, then cosine of (m∠BAC) = cosine of (m∠CAB) (Substitution)
4	cosine of (m∠CAB) = (distance BA) / (distance CA)	if cosine of (m∠BAC) = cosine of (m∠CAB) and cosine of (m∠BAC) = (distance BA) / (distance CA), then cosine of (m∠CAB) = (distance BA) / (distance CA) (Transitive Property of Equality Variation 2)

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