Re: [MATHEDCC] signed numbers
Barbara Lacey (laceyb@aurora.sunyocc.edu)
Tue, 9 Nov 1999 22:15:59 -0500 (EST)
If you were in the military you might appreciate the explanation I give
to my students about multiplying two negatives. If you do an about-face
you are facing backwards (or the negative of facing front). If you do
another about-face you are now facing forward again (or the positive
again). Therefore, an about-face about-face (or a double negative) is a
positive (or you are facing forard again).
Once I give the students the rule for multiplying two negatives
resulting in a positive they want to use to get a positive when adding two
negatives. I tell them that when they find a bank that when you bounce a
$10 check and a $15 check records a positive $25 in your account, please
let me know so I can bounce two checks. They see the absurdity of this
example and hopefully they remember it.
Babs
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