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# Why does -1 x -1 = +1? Watch

1. Like most of maths, it just does.

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2. because the two minuses cancel eachother out and become positive if it were -1x1 it would equal -1
3. (Original post by pseudonymegg)
because the two minuses cancel eachother out and become positive if it were -1x1 it would equal -1
I think OP means why is that true. If you had minus one lemon and multiplied it by another -1 lemon why would you then have one lemon?

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4. Because minus signs indicate a negative entropy change and hence negative energy. It's like antimatter basically and when antimatter collides (multiplication) you get matter (positive energy). This is basically why.

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5. (Original post by Straw-man666)
Because minus signs indicate a negative entropy change and hence negative energy. It's like antimatter basically and when antimatter collides (multiplication) you get matter (positive energy). This is basically why.

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Makes sense but entropy only been around since the 19th century. I'd assume the laws of multiplication were around much before then?

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6. (Original post by Straw-man666)
Because minus signs indicate a negative entropy change and hence negative energy. It's like antimatter basically and when antimatter collides (multiplication) you get matter (positive energy). This is basically why.

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not sure if srs or troll...
7. (Original post by Numberwang)
A negative and a negative= a positive (when you multiply and divide)

I'm not sure if OP means this ^ or why what I answered works. :/
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8. (Original post by Kabulkid)
not sure if srs or troll...
I'm not sure if YOU'RE being srs or troll...
9. (Original post by Straw-man666)
Because minus signs indicate a negative entropy change and hence negative energy. It's like antimatter basically and when antimatter collides (multiplication) you get matter (positive energy). This is basically why.

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It's too early in the morning for this level of intellectualism

Oh wait it's half 4.
10. (Original post by Afghan Warrior)
I'm not sure if YOU'RE being srs or troll...
im always srs.....wbu?
11. (Original post by Numberwang)
on a serious note:

i don't think anyone knows why but it seems to work, if we did maths when -1x-1=-1 then it wouldn't work out, it would give us crazy results.
12. The proper reason is a little complicated. Wikipedia has a light explanation here: http://en.wikipedia.org/wiki/Multiplication#Axioms

Essentially to define negative numbers you use ordered pairs (x,y) which translate into an integer x-y. That means each integer is represented by an infinite set of ordered pairs, e.g. -1 is the set {(0,1), (1,2), (2,3), ...}.

So to calculate -1 x -1 you first translate it into (0,1) x (0,1), and use the definition of multiplication for ordered pairs (that's a mouthful - the Wiki page has the formula for this) to find the result is (1,0), which then translates back into 1.
13. Yeh why. Like nobody ever explained why
14. As mentioned above, this is a consequence of the field axioms
15. It can be understood with complex numbers; On a diagram which lists the real part of a complex number on the x axis, and its imaginary part on the y axis (called an Argand diagram), a complex number is a point on this diagram, which is often described by the length of the line joining this point to origin (called its magnitude or modulus), and the angle that this line is at compared to the x axis, called the argument.

Now, when we multiply two complex numbers together, it can be shown that the result has a modulus that is the product of the first two moduli, but more importantly, the argument or angle of the two numbers are added.
So -1 has an angle of 180 degrees compared to the positive part of the x axis, so if we multiply -1 by -1, we add the two angles, 180 + 180 giving us 360 degrees, which takes us back around to positive one.

Ok that may have been long winded and confusing, but it's at least one explanation. As I understand it there's another, more fundamental reason that can be shown through set theory, but I don't know it.
16. (Original post by james1211)
Like most of maths, it just does.

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Yup. Let the mathematicians worry about it.
17. (Original post by Kabulkid)
im always srs.....wbu?
i'm srs too.
High five. Brohime.
18. So many bad answers here, saying that minus x minus=+ is not helping.

Here is an explanation:

(-1)*(-1)-1
=(-1)*(-1)+(-1)
=(-1)*(-1+1) (I have just factorised here.)
=(-1)*0
=0
19. (Original post by Afghan Warrior)
i'm srs too.
High five. Brohime.
*high five*

hows life? (im expecting an elaborate answer)..

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