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Subject: "Can anyone proves the following question?"     Previous Topic | Next Topic
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albert1950
Member since May-30-08
Jul-09-08, 07:53 AM (EST)
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"Can anyone proves the following question?"
 
   ALBERT FROM TAIWAN
Can anyone proves the following questions ?
(1.)A negative number multiplied by a negative number the result will
be positive.
(2.)A negative number multiplied by a positive number the result will
be negative.


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alexbadmin
Charter Member
2244 posts
Jul-09-08, 08:01 AM (EST)
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1. "RE: Can anyone proves the following question?"
In response to message #0
 
   Neither is a matter of proof but of definition.

There is a great convenience in having these properties because then the general formulas that work when all quanitties are positive remain valid when some or all of them are allowed to be negative.

For example,

(a + b)c = ab + ac

Allowing for a negative, say, b

0 = (a - a)c = ac - ac = 0

fits nicely. But, again, the latter is a matter of definition, not of a derivation.


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