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