02GF74
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| posted on 7/10/08 at 04:23 PM |
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simple maths question
Why does a negative number multiplied by another negative number give a positive number?
Anyone know, other than we were told this by our teachers, but why is it so?
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mookaloid
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| posted on 7/10/08 at 04:27 PM |
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it's the law 
"That thing you're thinking - it wont be that."
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mikeb
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| posted on 7/10/08 at 04:28 PM |
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Imagine the number line. Suppose on the left it starts -6, -5, -4, -3, -2, -1, 0, +1, +2, +3, etc.
Let's calculate 2 x (-3).
The expression -3 says starting at zero, go left 3 steps. The expression 2 x means do it twice.
Where do you finish? -6
If you see why you finish on the left side, you have your answer.
What about minus x minus. Let's calculate (-2) x (-3).
Again -3 says starting at zero go left 3 steps. The expression -2 x means, no, go the other way instead -- twice.
Where do you finish? +6. Minus x minus = plus.
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Paul TigerB6
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| posted on 7/10/08 at 04:28 PM |
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It just is ok!!!!
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mikeb
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| posted on 7/10/08 at 04:29 PM |
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still think its a crud answer
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mikeb
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| posted on 7/10/08 at 04:31 PM |
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http://hartvig.com/2006/8/21/simple_math_minus_multiplied_minus_equals_plus.aspx
Right time to go home...
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liam.mccaffrey
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| posted on 7/10/08 at 04:36 PM |
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if you say -6 x -4 and you think of it as having
-6 groups of -4.
thats -(-4) -(-4) -(-4) -(-4) -(-4) -(-4)
then if you say double negative is positive for each of the pairs of - signs then you have
+4+4+4+4+4+4=24
[Edited on 7/10/08 by liam.mccaffrey]
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omega0684
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| posted on 7/10/08 at 04:37 PM |
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mathematical law, (-) x (-) = (+)
god i love WIKI answers
minus times a minus equals a plus linky
it has to be the most un-mathematical answer ever!
[Edited on 7/10/08 by omega0684]
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coozer
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| posted on 7/10/08 at 04:42 PM |
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So if I go into the garage and say.. I've got -3 engines over there and I'm sure theres another -2 somewhere when I come back will there
be 6? but how do I do the X thing practically to make 6 engines happen?
1972 V8 Jago
1980 Z750
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BenB
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| posted on 7/10/08 at 04:51 PM |
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For the same reason that a negative balance is an overdraught and a negative overdraught is a positive balance.
A lack of a lack is a positive balance.
That's not maths, just logic.
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liam.mccaffrey
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| posted on 7/10/08 at 04:54 PM |
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@ coozer
if you owed someone 3 engines you would have -3 engines. so if you then owed someone 3 engines minus 2 times, then you would indeed find yourself owed
6 engines
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clairetoo
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| posted on 7/10/08 at 05:05 PM |
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So..........if I have -£100 in the bank , and spend -£100 twice , I will then have +£100
I think I need to go and have a word with my bank manager 
Its cuz I is blond , innit
Claire xx
Will weld for food......
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eznfrank
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| posted on 7/10/08 at 05:50 PM |
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If you think that's a bit of a mystery you should try a bit of Ethiopian Shamen multiplication.
Pick two numbers which would be difficult to multiply in your head. Works with any number.
Eg 21 x 31. Put one number in the left column and one in the right. In the left column half the number and write the new number underneath. Forget
1/2's they don't exist (eg half of 17 would be 8, because 8.5 doesn't exist??) and keep doing this till you get to 1.
In the right hand side column keep doubling the number and writing it underneath so you have as many rows as you do for the first number.
Then, in the left column cross out any even numbers on account of them being "evil" and cross out their corresponding number in the right
column.
Then add up everything in the right column that hasn't been crossed out and you have your answer.
Eg.
21 x 31
10..........62 - discard this line as it's evil
5............124
2............248 - discard this line as it's evil
1............496
So you add, 31, 124 and 496 = 651 which is 21 x 31.
Weird eh!!!
[Edited on 7/10/08 by eznfrank]
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mr henderson
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| posted on 7/10/08 at 05:55 PM |
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quote:
Originally posted by liam.mccaffrey
@ coozer
if you owed someone 3 engines you would have -3 engines. so if you then owed someone 3 engines minus 2 times, then you would indeed find yourself owed
6 engines
I think that's the best answer so far
John
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liam.mccaffrey
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| posted on 7/10/08 at 06:01 PM |
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quote:
Originally posted by clairetoo
So..........if I have -£100 in the bank , and spend -£100 twice , I will then have +£100
I think I need to go and have a word with my bank manager
Claire you are exactly right, if you spent -£100 twice your bank balance would increase by £200
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adithorp
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| posted on 7/10/08 at 06:24 PM |
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quote:
Originally posted by liam.mccaffrey
quote:
Originally posted by clairetoo
So..........if I have -£100 in the bank , and spend -£100 twice , I will then have +£100
I think I need to go and have a word with my bank manager
Claire you are exactly right, if you spent -£100 twice your bank balance would increase by £200
Because we refer to spending -£100 as selling something for £100.
adrian
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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blakep82
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| posted on 7/10/08 at 06:27 PM |
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double negative = postive no means yes and all that...
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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24vseven
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| posted on 7/10/08 at 07:13 PM |
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so here you go
if 2 to the power 2 (2x2) is 4
2 to the power 3 (2x2x2) is 8
whats 2 to the power 0
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liam.mccaffrey
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| posted on 7/10/08 at 07:17 PM |
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anything to the power of 0 is 1
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24vseven
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| posted on 7/10/08 at 07:21 PM |
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quote:
Originally posted by liam.mccaffrey
anything to the power of 0 is 1
again why
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blakep82
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| posted on 7/10/08 at 07:24 PM |
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^^
quote:
Originally posted by mookaloid
it's the law
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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Alan B
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| posted on 7/10/08 at 07:56 PM |
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quote:
Originally posted by 24vseven
quote:
Originally posted by liam.mccaffrey
anything to the power of 0 is 1
again why
X^2 x X^2 = X^4 (exponents added)
X^2 /X^2 = 1
Following the first example 2+2=4
So, 2-2=0
Therefore X^0 = 1
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24vseven
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| posted on 7/10/08 at 08:38 PM |
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quote:
Originally posted by Alan B
quote:
Originally posted by 24vseven
quote:
Originally posted by liam.mccaffrey
anything to the power of 0 is 1
again why
X^2 x X^2 = X^4 (exponents added)
X^2 /X^2 = 1
Following the first example 2+2=4
So, 2-2=0
Therefore X^0 = 1
ok just checking lol
so therefor what is -4 to the power 0.5
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liam.mccaffrey
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| posted on 7/10/08 at 09:08 PM |
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i can see where this is going
(-4)^0.5=sqrt(-4)=sqrt(4) x sqrt(-1)=2i
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24vseven
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| posted on 7/10/08 at 09:10 PM |
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and to finish
i=?
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