How would you prove this little inequality?

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Discussion Overview

The discussion revolves around proving the inequality (1 + 1/n)^n ≤ e ≤ (1 + 1/n)^(n+1) without using power series for e. Participants explore various approaches and reasoning related to this mathematical inequality, focusing on the implications of limits and properties of sequences as n approaches infinity.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses difficulty in proving the inequality and requests hints for a proof without using power series.
  • Another participant suggests the limit as n approaches infinity of (1 + 1/n)^n equals e, implying this is a key aspect of the proof.
  • A different participant notes that for finite n, (1 + 1/n)^n is less than e, and as n approaches infinity, it equals e, while the right side is always greater than e for finite n.
  • One participant proposes reasoning that (1 + 1/n)^n must be less than (1 + 1/n)^(n+1) due to the positivity of the terms involved, suggesting a potential pathway for the proof.
  • Another participant mentions the use of power series for (1 + x)^n, indicating a method that is not permitted in this context.

Areas of Agreement / Disagreement

Participants do not reach a consensus on a specific proof method. There are multiple competing views on how to approach the proof, and the discussion remains unresolved regarding the best strategy to prove the inequality without using power series.

Contextual Notes

Participants express limitations in their current knowledge, particularly regarding the use of power series and the formal requirements for the proof. There is also an acknowledgment of the behavior of the inequality as n approaches infinity.

stunner5000pt
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i'm stuck trying to prove this little inequality:

(1+ 1/n)^n <= e <= (1+1/n)^n+1
is there a way to prove this without without resorting to power series for e (because we're not allowed to, and we don't know this yet) and also note that n is a natural number, (positive integer).
 
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Here's a hint:

[tex]\lim_{n \to \infty} \Big( 1 + \frac{1}{n} \Big)^n = e[/tex]

cookiemonster
 
ummmm

ok i know tha already i just don't know how to prove it give me hint on hwo to prove it
 
Just how formally do you want to prove it?

It's pretty easy to notice that for [itex]n<\infty[/itex], the left side is less than e. When [itex]n = \infty[/itex], it is exactly equal to e.

The same holds true for the right side, except that it's always greater than e except when [itex]n = \infty[/itex].

cookiemonster
 
You do it by power series for (1+x)^n valid when |x|<1 (ie x=1/n)
 
Originally posted by stunner5000pt
i'm stuck trying to prove this little inequality:

(1+ 1/n)^n <= e <= (1+1/n)^n+1
is there a way to prove this without without resorting to power series for e (because we're not allowed to, and we don't know this yet) and also note that n is a natural number, (positive integer).
Why can you not just reason that (1+1/n)^n has to be less than (1+1/n)^n * (1+1/n), as, until n => infinity, 1+1/n will always be a positive value above * a positive value that will always make the right hand larger.
 

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