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Why a double negative makes a positive. (Mathematics)

1st January 2010, 14:13
Post: #1




Why a double negative makes a positive. (Mathematics)
So after a discussion with TruthWorthy in another thread (where he attempted to show that a double positive made a negative), I looked into why a double negative makes a positive.
Essentially, we must first agree that a negative number is simply a positive number multiplied by 1. In other words, to get the negative of 2, we multiply by 1. 1 * 2 = 2. If we accept this as correct, then we can write the multiplication of two negative numbers like so: 2 * 3 = (1)(2)(1)(3) 2 * 3 = (1)(1)(2)(3) 2 * 3 = (1)(1) * 6 So, the question is, (1)(1) = ? The convention (1)(1) = +1 has been adopted because anything else causes the distributive property of multiplication to break for negative numbers. For example, let's assume (1)(1) = 1. (1)(1 + 1) = (1)(1) + (1)(1) (1 + 1) on the left equals 0, so the equation can be written: (1)(0) = (1)(1) + (1)(1) Since we agreed that any positive number multiplied by negative 1 is the negative form, and that (1)(1) = 1, we can further simplify this: (1)(0) = 1 + 1 So: 0 = 2??? If we place any other number (apart from +1) as the answer to the calculation (1)(1) = ?, the same thing happens. This is why two negatives make a positive in mathematics. Reproduced for your enjoyment from http://mathforum.org/dr.math/faq/faq.negxneg.html 

1st January 2010, 16:08
(This post was last modified: 1st January 2010 16:09 by Purple Rabbit.)
Post: #2




RE: Why a double negative makes a positive. (Mathematics)
Was your discussion with TruthWorthy about mathematics or logic?


"I'm like a rabbit suddenly trapped, in the blinding headlights of vacuous crap"  Tim Minchin in "Storm"
Christianity is perfect bullshit, christians are not  Purple Rabbit, honouring CS Lewis Faith is illogical  fr0d0 

1st January 2010, 17:19
Post: #3




RE: Why a double negative makes a positive. (Mathematics)
No idea, he seemed to bring ideas about both into it. Anyway, this thread is about mathematics, nothing else.


1st January 2010, 17:38
Post: #4




RE: Why a double negative makes a positive. (Mathematics)
im in year 10 now, you have no idea how much our teacher is stressing that 2 negatives equal a positive, and he never told us why, he just says "follow the rules and you'll pass the test" in a very jokingly kind of way, as if it would be to complicated to describe in 2 hours of maths lesson ¬.¬


Vampires will never hurt you.......


1st January 2010, 17:45
Post: #5




RE: Why a double negative makes a positive. (Mathematics)
Well there you have your answer. 2 negatives make a positive because otherwise all mathematical hell breaks loose.


Kudos given by (1): Alice 
1st January 2010, 17:59
(This post was last modified: 1st January 2010 18:00 by Ashes1995.)
Post: #6




RE: Why a double negative makes a positive. (Mathematics)
you got that right, if someone in our class said that 2 negatives equals a negative because they missed a lesson, our teacher would go freakoid berserko
then again we learned that in like year 7, so that would be the reason behind it 

Vampires will never hurt you.......


1st January 2010, 18:06
Post: #7




RE: Why a double negative makes a positive. (Mathematics)  
Kudos given by (1): EvidenceVersusFaith 
1st January 2010, 19:03
Post: #8




RE: Why a double negative makes a positive. (Mathematics)
NO ADRIAN! NOT AGAIN!!!


1st January 2010, 19:14
Post: #9




RE: Why a double negative makes a positive. (Mathematics)
So when she cries "No, no!" she means "Yes".


Only sheep need a shepherd.


Kudos given by (1): Alice 
1st January 2010, 21:48
Post: #10




RE: Why a double negative makes a positive. (Mathematics)
Lol! I'm so going to use that...
Would it stand up in court? "Your honor, my client was simply confused by her illogical use of a double negative!" yay Pope! Rhizo 

Kudos given by (1): Alice 
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