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#1 2006-02-24 11:04:09

mikau
Member
Registered: 2005-08-22
Posts: 1,504

who woulda thunk it?

The limit of the nth root of n as n approaches infinity equals.... 1!!! I don't know about you guys but I find this extremely remarkable!

The proof of this uses just a simple common technique. I'll use the method of finding the limit of ln (n^(1/n)) as n approaches infinity, and raising e to the power of that limit.

limit of ln (n^(1/n)) as n approaches infinity

= limit of 1/n ln( n) as n approaches infinity = limit of (ln n)/n as n approaches infinity ( =  ∞/∞) since this is an indeterminant form,  we use L' hopitals rule,   1/n / 1 = 1/n.  As n approaches infinity 1/n = 0.

e^0 = 1 so the limit of the the nth root of n as n approaches infinity is one! Thats just awsome! Check it on a calculator if you don't believe me.

Last edited by mikau (2006-02-24 11:06:24)


A logarithm is just a misspelled algorithm.

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#2 2006-02-24 11:20:38

mikau
Member
Registered: 2005-08-22
Posts: 1,504

Re: who woulda thunk it?

This reminds me of e in some ways. This seems to suggest 1^∞ = ∞ but this is impossible. Therefore it must be something like the limit of (1 + 1/x )^n as n approaches infinity and x is some function of n, and n does not equal x. (otherwise this would be e). I wonder if we could figure out the relation between n and x...


A logarithm is just a misspelled algorithm.

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#3 2006-02-24 11:56:37

ryos
Member
Registered: 2005-08-04
Posts: 394

Re: who woulda thunk it?

Given that 1/∞ = 0, it's not that surprising at all...


El que pega primero pega dos veces.

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#4 2006-02-24 12:15:39

mikau
Member
Registered: 2005-08-22
Posts: 1,504

Re: who woulda thunk it?

Yes and no. I mean, if you have 1/n, when n becomes significantly large, the exponant tends to be very small, but the base tends to get very large. Just like the definition of e.  limit of (1 + 1/x)^x as x approaches infinity. You're inclined to say 1/x = 0 and eliminate it, but the infinitely small difference, to the infinitieth power makes a difference. Likewise, I was inclined to believe the smallness of the exponant would be "canceled out" by the hugeness of the base.


A logarithm is just a misspelled algorithm.

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#5 2006-02-24 13:34:09

John E. Franklin
Member
Registered: 2005-08-29
Posts: 3,562

Re: who woulda thunk it?

I haven't tried to understand your explanations, but it isn't remarkable to me.
#*#=2
#*#*#=3
#*#*#*#=4
#*#*#*#*#=5
#*#*#*#*#*#=6
The #'s go up slowly, but multiplying is so powerful, why wouldn't you expect to
approach one from above?  I would.

'Course I can't remember L'Hopital's Rule by its name.  I have a lot to review.
Don't explain for me, I'll do some research...


igloo myrtilles fourmis

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#6 2006-02-24 17:04:44

mikau
Member
Registered: 2005-08-22
Posts: 1,504

Re: who woulda thunk it?

maybe you guys are more familiar with limits then me and it doesn't come to such a suprise.

At any rate, the reason I didn't conclude that from the start, I could have looked at the exponant 1/n and figured this comes to zero so its one no matter what, but singling out and isolating a piece of a limit and evaluating can be dangerous, ESPECIALLY when they are directly connected to infinitly large numbers. I repeat: In the definition of e: Limit of (1 + 1/n)^n as n approaches infinity. Your inclined to notice the 1/n term and rewrite it as zero, but this infinitly small fraction is raised to an infinitly large power! So it does make a difference! Here we have the reverse, an infinitly large number being raised to an infinitly small power. For all I knew it might have ended up being 1/e or something like that. Thats why I made no assumptions.

Like I said, when infinitly small and infinitly large come in contact, sometimes they "cancel eachother out" so isolating each individual limit can be dangerous. Don't you agree?

Last edited by mikau (2006-02-24 17:40:58)


A logarithm is just a misspelled algorithm.

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#7 2006-02-25 05:54:40

John E. Franklin
Member
Registered: 2005-08-29
Posts: 3,562

Re: who woulda thunk it?

.99 ^ big number, goes down.
1.01^ big number, goes up.


igloo myrtilles fourmis

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#8 2006-02-25 06:12:30

Ricky
Moderator
Registered: 2005-12-04
Posts: 3,791

Re: who woulda thunk it?

I'm not really suprised at 1, but I really like the way mikau took the limit.  Never would have thought of doing that.


"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."

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#9 2006-02-25 08:22:47

mikau
Member
Registered: 2005-08-22
Posts: 1,504

Re: who woulda thunk it?

you mean taking the natural log, finding the limit, and raising e to that power? Thats a pretty common technique in my mathbook.

Anyways, the title of this thread is "who woulda thunk it?" clearly the answer is "everyone woulda thunk it.... except mikau..."

I feel stupid...

Last edited by mikau (2006-02-25 08:29:18)


A logarithm is just a misspelled algorithm.

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#10 2006-02-25 09:46:56

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

Re: who woulda thunk it?

Wait a minute...

It was shown somewhere else that this equation:

Had the solution of x = the nth root of n.

Surely, what you've just said means that:


Why did the vector cross the road?
It wanted to be normal.

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#11 2006-02-26 06:07:55

mikau
Member
Registered: 2005-08-22
Posts: 1,504

Re: who woulda thunk it?

now I'm confused.

technically the limit I found seems to suggest 1^∞ = ∞ but this is obviously not true. This is just the limit. 1 to any power = 1 no matter what. The nth root of n as n approaches infinity, tends to be 1, but 1 is the limit, it can never equal 1.


A logarithm is just a misspelled algorithm.

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#12 2006-02-26 08:35:50

MathsIsFun
Administrator
Registered: 2005-01-21
Posts: 7,535

Re: who woulda thunk it?

And, as John said, anything below 1 goes to 0.


"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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