Our server costs $25 per month to run. Please consider donating to help keep the site running. Help us gain new members by following us on Twitter and liking our page on Facebook!
Current time: 3rd May 2016, 02:54

Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Why a double negative makes a positive. (Mathematics)
#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
Reply
#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
Reply
#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.
Reply
#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.......Devil
Reply
#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.
Reply
#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.......Devil
Reply
#7
RE: Why a double negative makes a positive. (Mathematics)
Since you are new here, did you also know that 0.9... = 1

Tongue

http://atheistforums.org/thread-1989.html
Reply
#8
RE: Why a double negative makes a positive. (Mathematics)
NO ADRIAN! NOT AGAIN!!!
Reply
#9
RE: Why a double negative makes a positive. (Mathematics)
So when she cries "No, no!" she means "Yes".
Only sheep need a shepherd.
Reply
#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
Reply


Possibly Related Threads...
Thread Author Replies Views Last Post
  Cooking with Dyre Double Recipe Late night munchies + Bread pudding dyresand 0 267 13th November 2015, 02:50
Last Post: dyresand
  A question about race and double standards in Humans Dystopia 33 1496 23rd September 2015, 17:23
Last Post: Minimalist
  double post Thena323 14 826 3rd September 2015, 07:19
Last Post: Pandæmonium
  double post vorlon13 1 307 2nd September 2015, 23:31
Last Post: vorlon13
  What a difference a rum makes Razzle 2 322 19th April 2015, 05:05
Last Post: Razzle
  Having a case of double depression JosephBowie 8 1773 21st April 2013, 06:39
Last Post: Aractus
  What Makes You Assume That I'm a Troll? RonaldReagansGhost666 11 1880 20th January 2013, 07:23
Last Post: Stimbo
  Satan Makes Everything Sexier thesummerqueen 37 4117 14th November 2011, 07:21
Last Post: Zen Badger
  Humanity makes me want to puke.;;help ? Rwandrall 22 4644 8th June 2011, 17:02
Last Post: Moros Synackaon
  A positive result for alcohol. ib.me.ub 9 1677 6th November 2010, 22:49
Last Post: ib.me.ub



Users browsing this thread: 1 Guest(s)