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2 Posts

Posted - 08/30/2007 :  18:34:15  Show Profile
I know that when you are solving an inequality that involves multiplying to deviding by a negative you have to flip the inequality sign but I do not understand why. Could someone please help me understand this?
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Advanced Member

2399 Posts

Posted - 08/30/2007 :  18:43:46  Show Profile
3 > -1
Multiply both sides by -1,
-3 < 1

You got it?
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Advanced Member

1470 Posts

Posted - 08/31/2007 :  07:33:40  Show Profile
Another difficult concept involves division by a number between 1 and -1. The beginning math student gets confused. Just when they understand that division results in a smaller number, they find out that is not always the case.
and so on.
However, look at something like
You end up with a bigger number than you started with.
Think about why and it will help you.

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Advanced Member

1470 Posts

Posted - 08/31/2007 :  13:36:32  Show Profile
Yes, that is what I was pointing out. I wanted mandm87 not to get frustrated if still did not understand after the explanations that you and sahsjing gave. Many things that seem simple are really more difficult.
Originally posted by David

12.75 = 16 might cause confusion because the rule for division by a fraction is generally [and necessarily] taught without explanation. That is so since it's basis lies in a more general knowledge of the number system, albeit in fundamental properties, and young people ready to learn by rote are not ready to encompass that just yet. If there is a problem it is in that the basis for the rule for fractions is not taught later on either, for the most part.

It's easier to explain algebraically if the decimal [.75] is seen as a fraction [3/4]..."If this is 3/4 of that, then that is 4/3 of this." It's still not simple to see in terms of physical division of blocks, as in aliquot parts.

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