Proof: Multiply by 2
Let's prove the following theorem:
if the following are true:
- a ⋅ 2 = b
- not (2 = 0)
then a = b ⋅ (1 / 2)
Proof:
Given
| 1 | a ⋅ 2 = b |
|---|---|
| 2 | not (2 = 0) |
| # | Claim | Reason |
|---|---|---|
| 1 | (a ⋅ 2) ⋅ (1 / 2) = b ⋅ (1 / 2) | if a ⋅ 2 = b, then (a ⋅ 2) ⋅ (1 / 2) = b ⋅ (1 / 2) |
| 2 | (a ⋅ 2) ⋅ (1 / 2) = a | if not (2 = 0), then (a ⋅ 2) ⋅ (1 / 2) = a |
| 3 | a = b ⋅ (1 / 2) | if (a ⋅ 2) ⋅ (1 / 2) = b ⋅ (1 / 2) and (a ⋅ 2) ⋅ (1 / 2) = a, then a = b ⋅ (1 / 2) |
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