why a negative times a negative is a positive?

>>7924562
Because -a * -b = (-1) * a * (-1) * b = a * b
faggot

>>7924562
Multiplication is addition

>>7924571
incorrect.
gaylord

>>7924571
sooooo how am I supposed to add -1, -1 times?

>>7924569
Why (-1)(-1) = 1, faggot?

>>7924574
-3 * -4 = (-1) * 3 * (-1) * 4 = 3 * 4 = (3 + 3 + 3 + 3) = 12
idiot

if you have to ask this the explanation would go over your head

go read a book on fields/abstract algebra

>>7924575
Because that's the definition of negation over multiplication in a field.
faglord

>>7924584
>it's true because of the field axioms
You must be a geometer, because that reasoning is circular.

>>7924620
nothing in mathematics is 'true', obviously you're not a mathematician or a good one at least

Is there a brief/condensed version of a proof for -1.-1=1

>>7924629
Yes. (-1) * (-1) = -(-1) = 1 lmao
let M be the multiplicative identity. [math]M^{-1}*M^{-1} = M^{-1 -1} = M[/math]

>>7924631
forgot parenthesis.

[math]M^{-1}*M^{-1}=(M^{-1})^{-1} = M[/math]

put your socks on
then put your shoes on

what do you do to get back to your feet?
take your shoes off
and then take your socks off

>>7924632
that implies [math]A*B = B^{-1}*A^{-1}[/math] actually. if someone wants to figure out how that relates to [math](-1)^2=1[/math] be my guest.

>>7924584
>Write axiom
>QED
Thanks for the contribution

>>7924644
Just visualize it. What's the area of a square with one corner on the origin and one corner at (-1,-1)? It's a 1 by 1 square.

>>7924652
>>7924632
kk thanks

>>7924575
Because (-1) + 1 = 0, and -x is defined to be the number such that x + (-x) = 0.

>>7924562
Why do you make this thread every day?

>>7924741
Writing more than 30 words in a 4chan post is the highest form of autism.

>>7924772
http://niceme.me/

>>7924741
Because multiplication by i is a counterclockwise rotation by π in the complex plane

You absolute plebs.

1 + -1 = 0
(1 + -1) * (1 + -1) = 0
1 - 2 + (-1)^2 = 0
(-1)^2 = 1.

It follows by commutativity of multiplication that any negative times a negative is positive.

If [math] z_1=(r_1, pi)[/math] and [math]z_2=(r_2, pi) [/math]then [math]z_1z_2=(r_1r_2, 2pi) [/math] which is obviously a positive number according to De Moivres formula.

>>7924652
>Just visualize it.
I just realized that was an incredibly wrong way for me to explain that, as a point at (-1,1) or (1,-1) would have an area of 1 even though multiplying them gives you -1.

You absolute plebs, "explaining" the proposition with complex-analytic formulas whose derivations assume the proposition.

>>7924763
Lmao look at this fucking nerd

If x+y=0, then y=y+0=y+(x-x)=(x+y)-x=-x.

So, therefore -x+(-(-x))= 0, then -(-x)=x.

>>7924562
you owe somebody 10 doll hairs.

when you increase that amount by multiplying more debt, say -10 more doll hairs the end result is the positive doll hairs, which is what you owe them

>>7925277
You need to prove that 1 - 1 = 0

xDDDDD

>>7924620
>>7924652
>>7924741

>All these people choose to use a well defined number system

If you have problems with this, you are free to count dollar bills in a number system that forms a non-commutative ring. Just don't ask why multiplication order matters and ignore the answer "because you're using a non-commutative ring."

>>7924562
Just is. Don't look behind the curtain.