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Re: negative * negative
Posted:
Apr 3, 1996 8:53 AM
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I'm surprised no one has mentioned the following. (I have heard it explained
this way several times; I feel there are some disadvantages to it, but I'll
let others articulate them if they so desire.)
In mathematics, definitions that are difficult to apply to concrete models
often are developed to be consistent with already established patterns.
(Aside: In higher arithmetic, for example, we expand nonnegative integer
exponents into negative integer exponents and then to rational exponents.)
We agree that positive times negative is negative (yes?). Then, for
example,
3*-3=-9
2*-3=-6
1*-3=-3
0*-3=0
In each case when we add subtract one to the first factor, the product is
increased by 3. Now, to keep the pattern consistent, -1*-3 must be....
(Of course, the introduction would have to be reworded for elementary
students....) Comments? Is this just as bad as "that's the rule"?
Eric Karnowski
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