Proof: Add Number to Both Sides

Let's prove the following theorem:

Proof:

Proof Table

#	Claim	Reason
1	180 = a + 90	if a + 90 = 180, then 180 = a + 90 (Symmetric Property of Equality)
2	180 + (90 ⋅ (-1)) = a	if 180 = a + 90, then 180 + (90 ⋅ (-1)) = a (Subtract Both Sides)
3	a = 180 + (90 ⋅ (-1))	if 180 + (90 ⋅ (-1)) = a, then a = 180 + (90 ⋅ (-1)) (Symmetric Property of Equality)
4	a = 90	if a = 180 + (90 ⋅ (-1)), then a = 90 (Subtraction Example 2)

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