Author 
Topic 

mandm87
New Member
USA
2 Posts 
Posted  08/30/2007 : 18:34:15

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? 


sahsjing
Advanced Member
USA
2399 Posts 
Posted  08/30/2007 : 18:43:46

3 > 1 Multiply both sides by 1, 3 < 1
You got it? 


the_hill1962
Advanced Member
USA
1470 Posts 
Posted  08/31/2007 : 07:33:40

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. 122=6 6015=4 10075=4/3 and so on. However, look at something like 12.75=16 You end up with a bigger number than you started with. Think about why and it will help you.



the_hill1962
Advanced Member
USA
1470 Posts 
Posted  08/31/2007 : 13:36:32

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.
quote: 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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