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- Thread starter ron_jay
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>Is it not possible to define in anyway such indeterminate quantities?

Sure, as x approaches 0, sin x approaches 0 while sin x / x approaches 1.

sin x / (x*x) approaches is "undefined" (i.e. it approaches plus or minus infinity) as real x approaches 0.

So, 1 / (x*x) at x = 0 is a much larger infinity than 1/x at x = 0. The former has a double pole there while the latter has a simple pole. The magnitude of the former infinity is essentialy the square of the latter, within some complex number factor.

You can also say that d/dx (x*x) = ((x+dx)*(x+dx)-x*x)/dx = 2x + dx where dx is an infinitesimal quantity equal to 1 / infinity. Or you can round it off to d/dx (x*x) = 2x.

Usually intuition suffices, but if you want to do this stuff rigorously, look into non-standard mathematics where

one can use the compactness theorem to shoehorn an infinitesimal quantity into the real number system.

>Is there actually any absolute zero quantity

Yes, it's denoted by 0 and its the quantity that when multiplied by any finite quantity yields 0. If you are dealing with times/positions/temperatures where you can choose to call some arbitrary measurement "0" then you've left the realm of pure numbers.

>does infinity ever tend toward finite grounds?

Yes, the sequence 1/5, 1/4, 1/3, 1/2, 1/1, 1/0, 1/-1, 1/-2, 1/-3, etc. shows how a positive quantity can grow, become infinite and then suddenly become negative. In this case plus/minus infinity appears between the positive and negative numbers. Other interesting examples of infinity becoming finite include zeta(-1) = 1 + 2 + 3 + 4 + 5 + ... = -1/12 and also exp(-zeta'(0)) = 1 * 2 * 3 * 4 * 5 * ... = sqrt(2 * pi)

Sure, as x approaches 0, sin x approaches 0 while sin x / x approaches 1.

sin x / (x*x) approaches is "undefined" (i.e. it approaches plus or minus infinity) as real x approaches 0.

So, 1 / (x*x) at x = 0 is a much larger infinity than 1/x at x = 0. The former has a double pole there while the latter has a simple pole. The magnitude of the former infinity is essentialy the square of the latter, within some complex number factor.

You can also say that d/dx (x*x) = ((x+dx)*(x+dx)-x*x)/dx = 2x + dx where dx is an infinitesimal quantity equal to 1 / infinity. Or you can round it off to d/dx (x*x) = 2x.

Usually intuition suffices, but if you want to do this stuff rigorously, look into non-standard mathematics where

one can use the compactness theorem to shoehorn an infinitesimal quantity into the real number system.

>Is there actually any absolute zero quantity

Yes, it's denoted by 0 and its the quantity that when multiplied by any finite quantity yields 0. If you are dealing with times/positions/temperatures where you can choose to call some arbitrary measurement "0" then you've left the realm of pure numbers.

>does infinity ever tend toward finite grounds?

Yes, the sequence 1/5, 1/4, 1/3, 1/2, 1/1, 1/0, 1/-1, 1/-2, 1/-3, etc. shows how a positive quantity can grow, become infinite and then suddenly become negative. In this case plus/minus infinity appears between the positive and negative numbers. Other interesting examples of infinity becoming finite include zeta(-1) = 1 + 2 + 3 + 4 + 5 + ... = -1/12 and also exp(-zeta'(0)) = 1 * 2 * 3 * 4 * 5 * ... = sqrt(2 * pi)

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Hurkyl

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This statement is not correct in the sense that you meant it. If something is undefined, then anything involving it is undefined. (In ordinary arithmetic) the statement "1/0=infinity" is undefined -- it is not true, nor is it false: it is nonsense. In ordinary arithmetic, there is nothing called "infinity", so that's another reason that assertion is nonsense.We know that anything divided by zero is 'undefined' or equal to infinity.

On the projective real line, there is something called "infinity". And in this context, 1/0 is not undefined: it is defined, and equal to infinity. Just to emphasize the point, that division symbol has a different meaning than it does in ordinary arithmetic. (Though the two usually agree)

On the extended real line, there is something called "positive infinity" and something called "negative infinity". In this context, 1/0 is undefined.

In the hyperreals, there is nothing called "infinity". But there are number

No it doesn't. In (usual) arithmetic, the concept of zero is something that satisfies the identities:The concept of zero basically refers to 'nothingness' or 'void', but that indeed has utmost importance in writing numbers.

0+x = x+0 = 0,

0x = x0 = 0.

It might be the case that in certain 0x = x0 = 0.

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12304 = 1*10,000 + 2*1,000 + 3*100 + 0*10 + 4*1

without zero you cannot have a positional number system, which is a major disadvantage (try multiplying in greek numerials, for instance).

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This should be moved to philosophy forum.

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HallsofIvy

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What about the people who philosophize about the difference between pure math and philosophy?

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matt grime

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Is there actually any absolute zero quantity and does infinity ever tend toward finite grounds?

Anyone who confuses that statement with pure maths is not a pure mathematician.

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What about the people who philosophize about the difference between pure math and philosophy?

From post 1:

Anyone who confuses that statement with pure maths is not a pure mathematician.

Ok. Lets have a definition of 'philosophy', without which all

Check this definition of philosophy from Wikipedia:

Philosophy is the discipline concerned with questions of how one should live (ethics); what sorts of things exist and what are their essential natures (metaphysics); what counts as genuine knowledge (epistemology); and what are the correct principles of reasoning (logic).[1] [2] The word itself is of Greek origin: φιλοσοφία (philosophía), a compound of φίλος (phílos: friend, or lover) and σοφία (sophía: wisdom).[3][4]

Though no single definition of philosophy is uncontroversial, and the field has historically expanded and changed depending upon what kinds of questions were interesting or relevant in a given era, it is generally agreed that philosophy is a method, rather than a set of claims, propositions, or theories. Its investigations are based upon reason, striving to make no unexamined assumptions and no leaps based on faith or pure analogy. Different philosophers have had varied ideas about the nature of reason, and there is also disagreement about the subject matter of philosophy. Some think that philosophy examines the process of inquiry itself. Others, that there are essentially philosophical propositions which it is the task of philosophy to prove.[5]

All Philosophy may not be true, but the truth remains the truth and thus there is no confusion between all that 'being a pure mathematician or not'

As said when a number is divided by zero, on an extended real line it is equal to infinity, then if you multiply infinity by 0, should it yield the number back?If not, then what is its solution?

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HallsofIvy

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Does that make him an impure mathematician?From post 1:

Anyone who confuses that statement with pure maths is not a pure mathematician.

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HallsofIvy

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All Philosophy may not be true, but the truth remains the truth and thus there is no confusion between all that 'being a pure mathematician or not'

As said when a number is divided by zero, on an extended real line it is equal to zero, then if you multiply infinity by 0, should it yield the number back?If not, then what is its solution?

The problem is not a question of philosophy or mathematics but rather your vague understanding of mathematics. Certainly

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On the projective real line, there is something called "infinity". And in this context, 1/0 is not undefined: it is defined, and equal to infinity. Just to emphasize the point, that division symbol has a different meaning than it does in ordinary arithmetic. (Though the two usually agree)

On the extended real line, there is something called "positive infinity" and something called "negative infinity". In this context, 1/0 is undefined.

Slip of the hand...anyway, then what exactly does any number divided by zero or inifinity yield or what is the product of zero and infinity?

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CRGreathouse

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It makes no sense to talk about either division or multiplication on the extended real number line.

Huh? Surely we can multiply and divide most elements by analogy with reals when real You still can't divide by zero, and can't multiply infinity by 0, but the rest can be defined in the ordinary way... yes?

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