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Current time: 26th November 2015, 02:55

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 Why a double negative makes a positive. (Mathematics) Tiberius Question Everything. Religious Views: Shell B Posts: 10650 Threads: 552 Joined: 25th August 2008 Reputation: 109 Why a double negative makes a positive. (Mathematics) 1st January 2010, 09:13 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 Purple Rabbit 26th Dimension Low Life Religious Views: Posts: 1317 Threads: 18 Joined: 7th December 2008 Reputation: 22 RE: Why a double negative makes a positive. (Mathematics) 1st January 2010, 11:08 (This post was last modified: 1st January 2010, 11:09 by Purple Rabbit.) 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 Tiberius Question Everything. Religious Views: Shell B Posts: 10650 Threads: 552 Joined: 25th August 2008 Reputation: 109 RE: Why a double negative makes a positive. (Mathematics) 1st January 2010, 12:19 No idea, he seemed to bring ideas about both into it. Anyway, this thread is about mathematics, nothing else. Ashes1995 Destroyer of worlds Religious Views: Wicca Posts: 227 Threads: 8 Joined: 28th December 2009 Reputation: 2 RE: Why a double negative makes a positive. (Mathematics) 1st January 2010, 12:38 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....... Tiberius Question Everything. Religious Views: Shell B Posts: 10650 Threads: 552 Joined: 25th August 2008 Reputation: 109 RE: Why a double negative makes a positive. (Mathematics) 1st January 2010, 12:45 Well there you have your answer. 2 negatives make a positive because otherwise all mathematical hell breaks loose. Ashes1995 Destroyer of worlds Religious Views: Wicca Posts: 227 Threads: 8 Joined: 28th December 2009 Reputation: 2 RE: Why a double negative makes a positive. (Mathematics) 1st January 2010, 12:59 (This post was last modified: 1st January 2010, 13:00 by Ashes1995.) 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....... Tiberius Question Everything. Religious Views: Shell B Posts: 10650 Threads: 552 Joined: 25th August 2008 Reputation: 109 RE: Why a double negative makes a positive. (Mathematics) 1st January 2010, 13:06 Since you are new here, did you also know that 0.9... = 1 http://atheistforums.org/thread-1989.html Rhizomorph13 One chip equals three bisquits Religious Views: Atheist Posts: 2878 Threads: 61 Joined: 30th June 2009 Reputation: 37 RE: Why a double negative makes a positive. (Mathematics) 1st January 2010, 14:03 NO ADRIAN! NOT AGAIN!!! Pope Alfred A smile, a song and an excommunication Religious Views: Strong atheist Posts: 144 Threads: 3 Joined: 19th November 2009 Reputation: 3 RE: Why a double negative makes a positive. (Mathematics) 1st January 2010, 14:14 So when she cries "No, no!" she means "Yes". Only sheep need a shepherd. Rhizomorph13 One chip equals three bisquits Religious Views: Atheist Posts: 2878 Threads: 61 Joined: 30th June 2009 Reputation: 37 RE: Why a double negative makes a positive. (Mathematics) 1st January 2010, 16:48 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 « Next Oldest | Next Newest »

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