Proof: Three Angles

Let's prove the following theorem:

if the following are true:

60 + (a ⋅ 2) = 180
not (2 = 0)

then a = 60

Proof:

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Given

1	60 + (a ⋅ 2) = 180
2	not (2 = 0)

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 180 + (60 ⋅ (-1)) = 120 and a ⋅ 2 = 180 + (60 ⋅ (-1)), then a ⋅ 2 = 120 (Transitive Property of Equality)
4	a = 120 / 2	if not (2 = 0) and a ⋅ 2 = 120, then a = 120 / 2 (Divide Each Side)
5	120 / 2 = 60	120 / 2 = 60 (Fixed Value Statement)
6	a = 60	if 120 / 2 = 60 and a = 120 / 2, then a = 60 (Transitive Property of Equality)

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