Proving 2^n < n without Equality: Why Ask?

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Discussion Overview

The discussion revolves around the inequality 2^n < n! for n ≥ 4, specifically questioning the reasoning behind a textbook's request to prove a weaker condition (2^n ≤ n!) instead of the strict inequality. Participants explore the implications of proving one inequality over the other and the potential for typographical errors in the textbook.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant successfully proved 2^n ≤ n! using induction but struggles to show 2^n < n! without equality.
  • Another participant confirms that if x < y, then x ≤ y holds true, suggesting that proving the strict inequality is sufficient.
  • Some participants argue that the textbook cannot contain a misprint, citing specific values (e.g., n=4) to illustrate the relationship between 2^n and n!.
  • One participant notes that the graphs of 2^n and n! indicate that they never equal each other for n ≥ 4.
  • There is mention of the factors of 2^n and n! as a point of consideration in the discussion.
  • A later reply suggests that while one equality may be a misprint, the condition n ≥ 4 is correct.

Areas of Agreement / Disagreement

Participants express differing views on whether the textbook contains a misprint, with some asserting it cannot be a mistake while others suggest it might be. The discussion remains unresolved regarding the reasoning behind the weaker condition requested by the textbook.

Contextual Notes

Participants reference specific values and graphical representations to support their claims, but there is no consensus on the nature of the textbook's request or the implications of the inequalities discussed.

pivoxa15
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In my maths textbook it asks to prove 2^n<=n! for all n>=4

I could prove it no problems using induction but could show 2^n<n! without the equality inequality.

My question is why would the textbook ask for a weaker condition? Is it a misprint?

If I can show < then it automatically implies <= holds as well doesn't it?
 
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If I can show < then it automatically implies <= holds as well doesn't it?
Yes, if x is strictly less than y, then x is certainly less than or equal to y. With regards to your former question, it might just be a typo- either way, you can solve the problem using induction.
 
It can't be a missprint. See what happens with n=4.

Daniel.

PS. Apparently, it can be a missprint.
 
Last edited:
dextercioby said:
It can't be a missprint. See what happens with n=4.

Daniel.

2^4=16 , 4!= 24, so 2^4<4!
 
I was only asking the relationship between 2^n and n!

Looking at the graphs for 2^n and n! it seems that no where is 2^n=n!

n>=4 is definitely correct.
 
Look at what are the factors of 2^n and the factors of n!...
 
There are two "=" signs in question. The first one is definitely a misprint but n>=4 is correct.
 

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