Proof: Three Angles

Let's prove the following theorem:

Proof:

Proof Table

#	Claim	Reason
1	a ⋅ 2 = 180 + (60 ⋅ (-1))	if 60 + (a ⋅ 2) = 180, then a ⋅ 2 = 180 + (60 ⋅ (-1)) (Add Term to Both Sides 7)
2	180 + (60 ⋅ (-1)) = 120	180 + (60 ⋅ (-1)) = 120 (Fixed Value Statement)
3	a ⋅ 2 = 120	if a ⋅ 2 = 180 + (60 ⋅ (-1)) and 180 + (60 ⋅ (-1)) = 120, then a ⋅ 2 = 120 (Transitive Property of Equality)
4	a = 120 / 2	if a ⋅ 2 = 120, then a = 120 / 2 (Divide Each Side)
5	120 / 2 = 60	120 / 2 = 60 (Fixed Value Statement)
6	a = 60	if a = 120 / 2 and 120 / 2 = 60, then a = 60 (Transitive Property of Equality)

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