Proof: Sum Equation
Let's prove the following theorem:
if (a + b) + c = d, then a + c = d - b
Proof:
Given
| 1 | (a + b) + c = d |
|---|
| # | Claim | Reason |
|---|---|---|
| 1 | a + b = b + a | a + b = b + a |
| 2 | (b + a) + c = d | if (a + b) + c = d and a + b = b + a, then (b + a) + c = d |
| 3 | a + c = d + (b ⋅ (-1)) | if (b + a) + c = d, then a + c = d + (b ⋅ (-1)) |
| 4 | d - b = d + (b ⋅ (-1)) | d - b = d + (b ⋅ (-1)) |
| 5 | a + c = d - b | if a + c = d + (b ⋅ (-1)) and d - b = d + (b ⋅ (-1)), then a + c = d - b |
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