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Geek Culture / Math Question

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17
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Posted: 25th Oct 2007 18:05
Quote: "a/a=1 not 0

0 =/= 1

therefore you're talking poo.

sarcasm?
"

I wondered who would be the first to spot that...

the rabi, Nancy DrewG and Sudoku Arts.

demons breath
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Posted: 25th Oct 2007 18:11
I presume we're not talking about neo here...

In that case, what does he actually say?

http://jamesmason01.googlepages.com/index.htm
Seppuku Arts
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Posted: 25th Oct 2007 18:28
Quote: "@Seppuku: Undefined doesn't mean 0. 0 is a definition of something.

For example, you want to know how many pixies are currently in Berlin. At the moment it is an undefined number. It could be 38972395, or it could be 17. However, if it was 0, you would know exactly how many pixies there were in Berlin - none.

I wonder how many pixies there are in Berlin?
"

Ah yes that does make sense now, hmm...I might take up a course in Maths after I finish uni - I mean it sounds more interesting here than school tried to make it (actually it was very dry at school)

But with 0/0 aren't we defining the first to values and then using them in a sum (I am right in saying here the '/' is for division and not a fraction, just to see that we're on the same boat?) then surely the answer is defined. I mean I have no number, I have no one to give them to, so nobody has any numbers...Surely the value is still defined with the result as it would be if it were 3/2? Or wait...it it because there is no one to give to, how who's the to receive the value? Or something like that?

I love Nancy DrewG, but not insert brain here
demons breath
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Posted: 25th Oct 2007 18:33
yeah / is division. But that's the same as a fraction. In a fraction it's the top number divided by the bottom number.

Quote: "I have no number, I have no one to give them to, so nobody has any numbers"


It sounds so much easier when you put it like that. But logically, by observation:

2/0.5=4
2/0.2=10
2/0.1=20
2/0.01=200
2/0.0001=20000
2/0.000000001=2000000000

getting higher as the number gets closer to 0 therefore approaching infinity. There isn't a limit on how high the number can get so logically it should be infinity.

http://jamesmason01.googlepages.com/index.htm
mamaji4
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Posted: 25th Oct 2007 18:41 Edited at: 25th Oct 2007 18:41
Definition of infinity:
infinity is larger than the largest number you can think of. And if you can think of any number larger than it or infinity, infinity is larger than that.
Osiris
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Posted: 25th Oct 2007 19:52
Lol I just realized this was my thread. I didnt even notice my name next to it.



Off topic

This is my first red thread!! w00t!

Your signature has been erased by a mod because it's larger than 600x120....
demons breath
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Posted: 25th Oct 2007 21:16
Quote: "Off topic"


Because the rest of this thread has been really on topic?

http://jamesmason01.googlepages.com/index.htm
ionstream
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Posted: 25th Oct 2007 21:30
Chris K is mostly right.

0/0 is called "Indeterminate form", meaning that you don't know what the value is. It might be 0 or 1 or possibly even infinity, but the point is that you cannot make any conclusions about the value of 0/0 without an equation.

Example:

Consider the equation

(x^2 + x - 6)/(x-2)

If you substitute 2 into the equation, the numerator and the denominator become 0, thus evaluating to 0/0. However, look at a graph and you will see that there is a valid number that would be at that point (and that it is actually a line). Factor the numerator to get:

((x+3)(x-2))/(x-2)

And then simplify to get:

x+3

Substitute 2 into that equation and viola, you get 5. That means that 0/0 in this equation is actually equal to 5.

I'm not making this up, ask a math teacher or google "indeterminate form."

That's not as bad as you think you said.
Osiris
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Posted: 25th Oct 2007 21:32
Well that was way off topic lol, technically this was all about math and why its complicated.



Disclaimer,
im not saying math is really really complicated.

Your signature has been erased by a mod because it's larger than 600x120....
demons breath
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Posted: 25th Oct 2007 21:37
@Ionstream: Crazy. That's most perplexing. I never thought of that before as all our textbooks say "for x=/=0"

http://jamesmason01.googlepages.com/index.htm
mamaji4
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Posted: 25th Oct 2007 22:49
Quote: "((x+3)(x-2))/(x-2)

And then simplify to get:

x+3"


If you substitute 2 in the above equation you get
5*0/0

You are assuming that 0/0 = 1
That is why you get the resultant answer 5*1 = 5
x/x evaluates to 1 if and only if x has a VALID determinate, multiplicative inverse 1/x
0 does not have a multiplicative inverse and so 0/0 does not evaluate to 1
There's your flaw, the same one I made.
ionstream
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Posted: 25th Oct 2007 23:06
You have ignored the "simplify" step (and the stuff I wrote before it), in that you need to substitute 2 into the simplified equation. I have already addressed the 0/0 that you get from substituting 2 into the original equation, and why it needs to be simplified to get the answer. I have never implied that 5*0/0 = 5.

That's not as bad as you think you said.
mamaji4
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Posted: 25th Oct 2007 23:10
When you cancel out the (x-2) in the numerator and the denominator of the expression you are basically assuming that 1/(x-2) is the multiplicative inverse of (x-2) That is how you "simplify" an expression. But this is true only for all x, x<>2
For x = 2 the expression (x-2)/(x-2) evaluates to 0/0, and the rest is history...
Seppuku Arts
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Posted: 26th Oct 2007 01:38
Wow, I'm stifled now...you guys are hardcore.

I think I'll leave it to the experts.

I love Nancy DrewG, but not insert brain here
Chris K
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Posted: 26th Oct 2007 04:05
Quote: "When you cancel out the (x-2) in the numerator and the denominator of the expression you are basically assuming that 1/(x-2) is the multiplicative inverse of (x-2) That is how you "simplify" an expression. But this is true only for all x, x<>2
For x = 2 the expression (x-2)/(x-2) evaluates to 0/0, and the rest is history..."


Nope... you can cancel them.

Just draw a graph of it (or get a computer to).

-= Out here in the fields, I fight for my meals =-
mamaji4
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Posted: 26th Oct 2007 09:40 Edited at: 26th Oct 2007 11:07
I always thought Mathematics was a definite science. I had no idea it was open to subjective interpretation, without the requirement of a proof.
In which cas I propose 2 = 1 and if anybody contests that I shall go on strike.


Enter the function (x^2 + x - 6)/(x-2) at the graphing calculator link below
http://my.hrw.com/math06_07/nsmedia/tools/Graph_Calculator/graphCalc.html

Note that the graph erroneously appears to be a continuous stratight line. Look to the right and you will see that for x = 2
the value of y is blank/indeterminate, because the code produced an overflow error.
If you use conventional analysis too(no need to plot a graph), you can demonstrate that the function is discontuous at x= 2
i.e. it does not assume any value for y, at x =2

To put it another way,
When simplifying the equation the exact formal steps would be
(x^2 + x - 6)/(x-2)
=((x+3)*(x-2))/(x-2)
= x+3 for x <> 2
If you don't put the condition x<>2 at step 3 it is not an accurate simplification
The trouble is high school math makes a lot of assumptions and simplifications without being accurate. This is one thing that cannot be avoided because high school students aren't expected to understand the intricacies of algebraic systems. However, when presenting a formal proof on an important theorem it is very essential to make sure you do not violate any of the formal rules of the subject.

On a side note, I think this has just shown that the math coprocessor is incapable of handling the expression 0/0 and gives a false overflow error.
I think we have found a hardware bug in every PC on planet earth.
Somebody call the press.
Ionstream is about to become famous.
Chris K
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Posted: 26th Oct 2007 11:19
Quote: "it does not assume any value for y, at x =2"


No, no, no.

It assumes the value of 5 at x = 2

Quote: "The trouble is high school math makes a lot of assumptions and simplifications without being accurate."


No offense, but do you actually know any Maths of a higher-than-high-school level?

-= Out here in the fields, I fight for my meals =-
mamaji4
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Posted: 26th Oct 2007 11:29 Edited at: 26th Oct 2007 11:31
What else can I say. You leave me speechless.
A no, no, no is very difficult to disprove or stand up against. All I can think of is to call my Mommy. Mommy, mommy lookit Chris, he's makin me cry...

Quote: "No offense, but do you actually know any Maths of a higher-than-high-school level?
"

I think, that's a question you could take a vote for on the forums. And if all who agree say Aye! and are in the majority I shall resign.
Chris K
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Posted: 26th Oct 2007 14:47
Do you know L'hopital's Rule? Because you can use it to find the value of fractions that tend to zero on the top and bottom, that will show you that the graph goes through ( 2, 5 ).

-= Out here in the fields, I fight for my meals =-
mamaji4
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Posted: 26th Oct 2007 15:16 Edited at: 26th Oct 2007 15:24
There is a huge difference between -> 0 and = 0, but I've gone into that before.
Ok. You win. I lose. Happpy?
And I haven't taken High School Math and don't know nothing about math. It was just a stroke of luck that I got an 800/800 in my GRE math, without attending High School
mamaji4
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Posted: 26th Oct 2007 15:38 Edited at: 26th Oct 2007 18:13
Use of L'Hopital's rule to evaluate Indeterminate forms:

Quote: "Evaluating indeterminate forms
The indeterminate nature of a limit's form does not imply that the limit does not exist, as many of the examples above show. In many cases, algebraic elimination, L'Hôpital's rule, or other methods can be used to manipulate the expression so that the limit can be evaluated.

For example, the expression x2/x can be simplified to x at any point other than x = 0. Thus, the limit of this expression as x approaches 0 (which depends only on points near 0, not at x = 0 itself) is the limit of x, which is 0.
"


Note the phrases
"In many cases, algebraic elimination, L'Hôpital's rule, or other methods can be used to manipulate the expression"
'manipulate the expression' is the key phrase here.

"(which depends only on points near 0, not at x = 0 itself)"
'not at x = 0' is the key phrase here.

Quote: " the graph goes through ( 2, 5 ).
"

Which means that for x = 2, f(x) = 5
Let f(x) = ((x+3)*(x-2))/(x-2)
= (5*0)/0
= 0/0
Which means f(x) evaluates to 0/0 and not 5
(Note that we are not taking the limit of the function f(x) as x->2
but trying to evaluate f(x) at x=2)
The "graph would go through (2,5) for the linear equation
f(x) = x + 3 which is the graph you see.
Chris K
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Posted: 26th Oct 2007 16:54
I'm sorry I don't know how to explain it to you differently... I'm not saying that you are a bad mathematician, I don't know how hard it is to score 800/800 in GRE but I imagine it is not easy, but that doesn't change the fact that you are definitely wrong in this case, the expression ( x + 3 )( x - 2 ) / ( x - 2 ), is blatantly determinable for x = 2, but you are claiming it is undefined (or equal to 0/0).

Quote: "'manipulate the expression' is the key phrase here."


Why? You are saying that like it is an illegal thing to do...?

Quote: "= (5*0)/0
= 0/0"


I'm sorry you just can't do algebra/aritmetic like that when you have a denominiator of zero... I mean seriously how can you put an equals sign there...?

Are you doing Maths at college then?

-= Out here in the fields, I fight for my meals =-
mamaji4
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Posted: 26th Oct 2007 16:57
lol Chris you win, I lose. I'm in first grade yet.
ionstream
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Posted: 26th Oct 2007 21:49
There's nothing wrong with the math coprocessor. Look at the table of values for the graph link you posted, it doesn't give a value for x=2. Computers don't give an overflow error for it, they give a "divide by zero" error.

That's not as bad as you think you said.
mamaji4
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Posted: 27th Oct 2007 10:02
ionstream, the previous post applies to you too.
I lose, you win.

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