Proof: Negative Exponent
Let's prove the following theorem:
if not (xm = 0), then x((-1) ⋅ m) = 1 / (xm)
Power to a negative number is 1 divided by the power to the inverse of the number. For example, 2-3 = 1 / 23
Proof:
Given
1 | not (xm = 0) |
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# | Claim | Reason |
---|---|---|
1 | x(m + ((-1) ⋅ m)) = (xm) ⋅ (x((-1) ⋅ m)) | x(m + ((-1) ⋅ m)) = (xm) ⋅ (x((-1) ⋅ m)) |
2 | m + ((-1) ⋅ m) = 0 | m + ((-1) ⋅ m) = 0 |
3 | x(m + ((-1) ⋅ m)) = x0 | if m + ((-1) ⋅ m) = 0, then x(m + ((-1) ⋅ m)) = x0 |
4 | x0 = 1 | x0 = 1 |
5 | x(m + ((-1) ⋅ m)) = 1 | if x(m + ((-1) ⋅ m)) = x0 and x0 = 1, then x(m + ((-1) ⋅ m)) = 1 |
6 | 1 = (xm) ⋅ (x((-1) ⋅ m)) | if x(m + ((-1) ⋅ m)) = 1 and x(m + ((-1) ⋅ m)) = (xm) ⋅ (x((-1) ⋅ m)), then 1 = (xm) ⋅ (x((-1) ⋅ m)) |
7 | x((-1) ⋅ m) = 1 / (xm) | if 1 = (xm) ⋅ (x((-1) ⋅ m)) and not (xm = 0), then x((-1) ⋅ m) = 1 / (xm) |
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