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Prove this easy problem!

 
 
Alap
 
Reply Thu 25 Aug, 2005 10:59 am
Prove that: Infinite square = Infinite cube.

Well answer is there ...its only brain's work!

(please do tell all the assumptions made).
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Type: Discussion • Score: 1 • Views: 1,037 • Replies: 15
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Vengoropatubus
 
  1  
Reply Thu 25 Aug, 2005 09:30 pm
Well, if infinity were a number instead of a concept this would probably be answerable but as stated it has no real answer.
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markr
 
  1  
Reply Fri 26 Aug, 2005 12:17 am
Are you asking for proof that an infinite square (RxR) has the same number of points as an infinite cube (RxRxR)?

They both have the same number of points as an infinite line (R).
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Alap
 
  1  
Reply Fri 26 Aug, 2005 04:51 am
Well.... you guys are supporting your answer logically..that Infinite square should be equal to Infinite Cube as Infinite itself means not finite so when you cube it or square it the result is same..

But I want a anatical answer, proved by mathematical equations, also showing whatever assumptions made.
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g day
 
  1  
Reply Fri 26 Aug, 2005 08:00 am
Sorry you seem to have mistated your question. As stated its false, a two dimensional square (area) can never equal a 3 dimensional cube (volume) unless its a point of volume or area 0.

I think you meant to say prove lim (x-> infinity) x^2 like the lim (x-> infinity) x^3 is infinity, which is of course proved by a trival proof by inspection.

The definition of convergence is given a function (x) if one chooses a large number K you can find a number q which is a (inverse) function of x, so that all numbers greater than q (= f-1(K) ) then f(q+ i) > K for positive i.

Its trivial to see this for any power series equal or greater than 1.

Your statement does not have precision in the answer unless you ask show both series don't converge. You have asked it ignoring volumes and areas implying "equals" which implies and ordered, contiguous sequence like 1, 2, 3 - which is a properties of numbers and hence they can be compared like 3 - 1 = 5 - 3 true or false. However infinities aren't numbers so you can't simply do numerical field operations (+, - , *, /, <, >. = etc) on them because they are not numbers. That is were most of the problems for lay people arise.

If you want to do maths with infinites you general express them in a sense that gives them a ranking and sequence - like a non convergent limit series and then manipulate or compare limit series which do have flow and direction.
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ebrown p
 
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Reply Fri 26 Aug, 2005 08:02 am
Agreeing with g__day. bm
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engineer
 
  1  
Reply Fri 26 Aug, 2005 08:56 am
I disagree with your premise.

If infinity^2 = infinity^3, then the limit of x^3/x^2 as x -> infinity should be 1. It clearly is infinity, not one, so infinity^2 is not the same as infinity^3.
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Alap
 
  1  
Reply Fri 26 Aug, 2005 09:56 am
Well I dont understand why you _day take the squares and cubes to the dimensional analysis!

The question does not need the use of Calculus at all.

Its simple, you can prove it by algebra.

Come on I am a Senior Mathematics Consutant and I understand what you guys think...

but I have posted this simple question to check how many guys have common sense.
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Alap
 
  1  
Reply Fri 26 Aug, 2005 09:57 am
Well I dont understand why you _day take the squares and cubes to the dimensional analysis!

The question does not need the use of Calculus at all.

Its simple, you can prove it by algebra.

Come on I am a Senior Mathematics Consutant and I understand what you guys think...

but I have posted this simple question to check how many guys have common sense.
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ebrown p
 
  1  
Reply Fri 26 Aug, 2005 10:31 am
I sure hope the punchline is good....


<<waits apprehensively>>
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Beena
 
  1  
Reply Thu 29 Dec, 2005 12:45 am
Anything infinite would lack definition. Since you couldn't define an infinite square, you would not be able to define an infinite cube. If there could be a finite square then the points and the sides of the square would give it definition and remove its infiniteness and so an infinite square would have neither definition, shape or substance. Holy!

God is playing games with me again. I said on some other forum somewhere that if you can measure 90cms using a 30cms ruler, then you can also meaure infinity.

I'll be back, later!
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vinsan
 
  1  
Reply Thu 29 Dec, 2005 03:04 am
engineer wrote:
If infinity^2 = infinity^3, then the limit of x^3/x^2 as x -> infinity should be 1. It clearly is infinity, not one, so infinity^2 is not the same as infinity^3.


I agree here....

Also Alap when u talk about infinity, the proofs need calculus based explanantion. Simple Algebra was never meant to deal with infinite sums.
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g day
 
  1  
Reply Thu 29 Dec, 2005 07:58 am
vinsan wrote:
engineer wrote:
If infinity^2 = infinity^3, then the limit of x^3/x^2 as x -> infinity should be 1. It clearly is infinity, not one, so infinity^2 is not the same as infinity^3.


I agree here....

Also Alap when u talk about infinity, the proofs need calculus based explanantion. Simple Algebra was never meant to deal with infinite sums.


God that is poor mathematics! What is the major (wrong) assumption you are playing with there to get your logic error? Just because a sequence is unbounded doesn't mean it can't interact with another unbounded series according to simple limit rules. Nor can you choose to ignore these rules. Your flaunting these limit series rules would allow limits of 1/x * lim x (meaning infinity times zero) are always equal to 1, spelling the death of mathematics.

The mistake made above falls into treating infinity like a number to push its implied properities onto all formulea generally and saying if they are infinite they are equal. Bad mistake. Infinity is not a number. Infinities can be 'sized' in number theory - meaning you rank limit series and growth rates of functions that generate infinities into certain classes of growth magnitude.

The question as stands is ambigous as I said. Does the author wish to proof and infinite 2 dimensional shape (square) is equalivalent to an infinite 3 dimension shape (cube) which it isn't. Does the author wish to show series x^2 and x^3 are unbounded and don't converge - this is true. Does the author wish to assume series x^2 and x^3 are not only unbounded and don't converge but are equal? Well this is planely false as the limit of x^2 / x^3 is zero whilst the limit of x^3 / x^2 is infinite, so they are obivously not equal.

I said it before - sloppy mathematics - sloppy precision in asking a vague, unclear question.

You can have sized infinities too which further let you be incorrect.
0 Replies
 
Beena
 
  1  
Reply Thu 29 Dec, 2005 11:43 am
Beena wrote:
Anything infinite would lack definition. Since you couldn't define an infinite square, you would not be able to define an infinite cube. If there could be a finite square then the points and the sides of the square would give it definition and remove its infiniteness and so an infinite square would have neither definition, shape or substance. Holy!

God is playing games with me again. I said on some other forum somewhere that if you can measure 90cms using a 30cms ruler, then you can also meaure infinity.

I'll be back, later!


So if we assume that anything with substance cannot be infinite, then our world being matter or substance must be finite. Substance will be finite because we can always measure it. Jeez! So if God is infinite then for sure God is an idea or thought or something we just don't understand.
0 Replies
 
g day
 
  1  
Reply Fri 30 Dec, 2005 04:57 pm
I can play with infinities too...

If god can observe our reality part of him must be within this universe

God has infinite power, or energy

Part of infinity is still infinity

So god therefore projects infinite power or energy into our universe

But E = mc^2 or m = E/c^2

So the fraction of God observing within our universe has mass too, roughly fraction of infinity / c^2 = infinity

Significant mass can cause a black hole and close spacetime, infinite mass would cause an infinite black hole in our universe.

So we live inside a blackhole caused by god peaking at us!

How many logic errors can you spot in that reasoning...
0 Replies
 
DrewDad
 
  1  
Reply Sat 31 Dec, 2005 04:00 pm
g__day wrote:
I can play with infinities too...

If god can observe our reality part of him must be within this universe

How so? I can observe inside of a house even when I am outside, provided there is an open window.

God has infinite power, or energy

Is this supposed to be one of your postulates?

Part of infinity is still infinity

Well, not always. The set of positive integers is infinite... the set of integers from 1 to 10 is not. All of the rest of your thought experiment falls apart after this one.

So god therefore projects infinite power or energy into our universe

But E = mc^2 or m = E/c^2

So the fraction of God observing within our universe has mass too, roughly fraction of infinity / c^2 = infinity

Significant mass can cause a black hole and close spacetime, infinite mass would cause an infinite black hole in our universe.

So we live inside a blackhole caused by god peaking at us!

How many logic errors can you spot in that reasoning...
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