Re: Elementary proof for -ve x -ve = +ve
- From: "Pubkeybreaker" <Robert_silverman@xxxxxxxxxxxx>
- Date: 3 Nov 2006 11:15:46 -0800
joyo wrote:
Pubkeybreaker wrote:
joyo wrote:
I once asked a prof for the proof and he told me that he doesnt have
one ( its a convention or something like that)
Is there an elementary proof for this (something high school students
could understand)? thanks
Sigh. You must have a very incompetent prof.
It is a *trivial* consequence of the distributive property.
We have:
1 - 1 = 0 agreed?
-1 *(1 - 1) = -1 * 0 = 0 agreed? (multiply both sides by -1)
-1 * 1 + -1 * -1 = 0 apply the distributive property.
Since -1 * 1 = -1, then what is -1 * -1???? QED
So you have proven from the inside, not from the outside. Can you first
prove that -1*1=-1,
1*1=+1. You must prove from the outside.
Huh? 1 is the MULTIPLICATIVE IDENTITY ELEMENT OF THE INTEGERS.
1* x = x for all x
.
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