Re: Why should -1 multiplied by -1 be plus 1 and not -1

From: Acid Pooh (poohonlsd_at_yahoo.com)
Date: 07/30/04 

Date: 30 Jul 2004 13:40:23 -0700

">parr\(*>" <gniKyruaL@tenretnitb.moc> wrote in message news:<ced5oc$i55$3@titan.btinternet.com>...
> This is a genuine question, but not mine. Some years ago, I knew a
> girl, of a certain age, who could not understand why. Nor could I
> find a logical/mathematical argument to show her. It's not that she
> rejected the agreed arithmetical result, it's just that her intuition
> told her that two minuses should not become positive.
>
> I didn't spend a lot of time in the process because we had mutually
> interesting things to discuss.
>
> This girl was no slouch, but did not have a mathematical aptitude.
> In fact to reassure herself that she had something above neck level,
> she had applied to and been accepted into Mensa.
>
> So here's the problem or you logic buffs: How would you present a
> case that
> -1 x -1 = +1
> to someone whose intuition told her that it really ought to equal -1?
>
> (If this intuition versus logic problem bears an uncanny resemblance
> to another topic, it may be intentional:)

Maybe I shouldn't be a teacher, or a father... If anyone asked me
this question, I'd say "What are you, an idiot?" It's easy to forget
how hard this stuff was once.

'cid 'ooh

PS - I think a short talk about the role of axioms in math, and then
the algebraic proof mentioned by other posters would be the best way.

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