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*To*: mcole@weber.ucsd.edu, "eXtended Mind, Culture, Activity" <xmca@weber.ucsd.edu>*Subject*: Re: [xmca] a minus times a plus*From*: Ed Wall <ewall@umich.edu>*Date*: Mon, 27 Apr 2009 19:16:32 -0400*Cc*:*Delivered-to*: xmca@weber.ucsd.edu*Domainkey-signature*: a=rsa-sha1; s=2007001; d=ucsd.edu; c=simple; q=dns; b=mk+gYXTMhNtNk6H4gDHrGjYtRpuNWm22eu8YJPYsSfX0gGexoTAHBR+/4gcPlLcTS 7NYdrFTwHNC/fGXJ4SAdw==*In-reply-to*: <30364f990904271547o5b4df21eifca69bf8318483f2@mail.gmail.com>*List-archive*: <http://dss.ucsd.edu/mailman/private/xmca>*List-help*: <mailto:xmca-request@weber.ucsd.edu?subject=help>*List-id*: "eXtended Mind, Culture, Activity" <xmca.weber.ucsd.edu>*List-post*: <mailto:xmca@weber.ucsd.edu>*List-subscribe*: <http://dss.ucsd.edu/mailman/listinfo/xmca>, <mailto:xmca-request@weber.ucsd.edu?subject=subscribe>*List-unsubscribe*: <http://dss.ucsd.edu/mailman/listinfo/xmca>, <mailto:xmca-request@weber.ucsd.edu?subject=unsubscribe>*References*: <30364f990904271547o5b4df21eifca69bf8318483f2@mail.gmail.com>*Reply-to*: "eXtended Mind, Culture, Activity" <xmca@weber.ucsd.edu>*Sender*: xmca-bounces@weber.ucsd.edu

Mike

3 x 1 = 3 2 x 1 = 2 1 x 1 = 1 0 x 1 = 0

x + a = 0 ('a' a natural number)

y = b ('b' a natural number)

xy + ay = 0 or substituting for y xy + ab = 0 so, by definition, xy is a negative number.

Ed On Apr 27, 2009, at 6:47 PM, Mike Cole wrote:

Since we have some mathematically literate folks on xmca, couldsomeoneplease post an explanation of why multiplying a negative number by a positive numbers yields a negative number? What I would really love is an explanationthat is representable in a manner understandable to old collegeprofessorsand young high school students alike. mike _______________________________________________ xmca mailing list xmca@weber.ucsd.edu http://dss.ucsd.edu/mailman/listinfo/xmca

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**Follow-Ups**:**Re: [xmca] a minus times a plus***From:*Mike Cole <lchcmike@gmail.com>

**Re: [xmca] a minus times a plus***From:*Wolff-Michael Roth <mroth@uvic.ca>

**References**:**[xmca] a minus times a plus***From:*Mike Cole <lchcmike@gmail.com>

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