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Topic: -1 x -1 ?
Replies: 29   Last Post: May 13, 2009 9:01 AM

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 Henry Posts: 1,089 Registered: 12/6/04
Re: -1 x -1 ?
Posted: Jan 22, 2009 3:54 AM

On 22 Jan, 01:51, Tay <wintct...@gmail.com> wrote:
> -1 *-1 = 1 huh?
> The minus (negative) signs cancel eachother out:
> (-1)(-1) = [(-)(-)](1x1) = (+)(1x1) = +1
> It's so simple.

How do you know the two negative signs cancel each other out in
multiplication?

With (-x) being the additive inverse of x in a [unitary] ring,
I would allow you (-(-x)) = x, i.e. (-x)+x = 0 and x+(-x) = 0.
You can also have 1*x = x, x*1 = x, x*0 = 0 and 0*x = 0.

Consider (-1)*1 + (-1)*(-1) = (-1) * (1+(-1)) = (-1) * 0 = 0.
But (-1)*1 = (-1).
So (-1) + (-1)*(-1) = 0 and so (-1)*(-1) = 1.

Date Subject Author
9/16/99 Guillermo Phillips
9/16/99 Ian A. Mason
9/16/99 Peter Percival
9/16/99 Dave Seaman
9/17/99 Steve Leibel
9/17/99 Dale Henderson
9/18/99 Peter Percival
9/18/99 Bill Taylor
9/18/99 John Savard
9/19/99 carel
9/20/99 Jon Haugsand
9/20/99 HH
9/20/99 Jon Haugsand
9/20/99 Jonathan Hoyle
9/20/99 Jim Hunter
1/21/09 Tay
1/21/09 mensanator
1/21/09 lwalke3@lausd.net
1/22/09 Henry
1/22/09 David R Tribble
1/22/09 Dave L. Renfro
1/22/09 mensanator
5/12/09 Kayama
5/12/09 mensanator
5/12/09 hagman
5/12/09 Bill Dubuque
5/12/09 Bill Taylor
5/13/09 Cobra
5/13/09 Cobra