Prove "1/4a+1)+(1/4b+1)+(1/4c+1) ≥ 1" With Fun Proof

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Discussion Overview

The discussion revolves around proving the inequality \((1/4a+1)+(1/4b+1)+(1/4c+1) \geq 1\) under the condition that \((1/a+1)+(1/b+1)+(1/c+1)=2\), where \(a\), \(b\), and \(c\) are positive real numbers. The scope includes mathematical reasoning and attempts at proof.

Discussion Character

  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant mentions the original problem was proposed by Sefket Arslanagic from the University of Sarevo.
  • Another participant provides a formula for \(a\) in terms of \(b\) and \(c\), but does not clarify how it relates to proving the inequality.
  • A different participant expresses confusion about the previous results and requests clarification on how they contribute to the proof.
  • One participant claims to have derived a formula through algebra, suggesting it allows for testing values of \(b\) and \(c\) to find corresponding \(a\) values, though they do not assert it proves the statement.
  • Another participant suggests moving the discussion to a different subforum for a more formal proof.
  • A participant presents a proof by testing specific values (0, 1, 1) and claims it satisfies both parts of the problem, though this approach is met with skepticism.
  • One participant describes using Lagrange multipliers to find extrema and identifies \(a = b = c = 1/2\) as a minimum point, asserting that this leads to \(f(1/2,1/2,1/2) = 1\).
  • Another participant acknowledges the validity of the Lagrange multipliers method as a potential proof approach.

Areas of Agreement / Disagreement

Participants express various methods and approaches to prove the inequality, but there is no consensus on a definitive proof. Some methods are met with skepticism, and the discussion remains unresolved regarding the validity of the proposed proofs.

Contextual Notes

Some participants' approaches rely on specific values or methods that may not universally apply, and there are unresolved questions about the correctness of the algebraic manipulations and the implications of the proposed proofs.

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First of all, This problem was proposed by Sefket Arslanagic, University of Sarevo.

Code:
Let a, b, c be positive real numbers such that

(1/a+1)+(1/b+1)+(1/c+1)=2

Prove that

(1/4a+1)+(1/4b+1)+(1/4c+1) greater than or equal to 1
 
Last edited:
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I get:

a = (1 - bc) / (2bc + b + c)
 
i'm not sure how you got your results or how it proves the statement. Can you explain this to me?
 
I got it by a bit of algebra. I don't claim it helps in proving the statement, but (if it's right, as I think it is) then it allows anyone to guess any two values for b and c, and find the corresponding value of a that satisfies the first equation.

It at least allows you to test the second formula for a few different values, to satisfy yourself that it's probably right before embarking on a proof.
 
Forward this to General Math subforum and I will prove it there.
 
Heres my *PROOF*

Any numbers that satisfy a b and c for the first part, have to do it for the second part or else the questions an idiot. Try 0, 1, 1. Works for both parts, the questions not stupid, the proof is complete :P
 
Good one!

I used the method of Lagrange multipliers to find the extreme of:

(1/(4a+1))+(1/(4b+1))+(1/(4c+1)) = f(a,b,c)

Subject to the constraint that

(1/(a+1))+(1/(b+1))+(1/(c+1)) = 2

This gives a = b = c = 1/2, and f(1/2,1/2,1/2) = 1

A quick check of some other points (like 0, 1, 1) shows that this is a minimum point.
 
That would work as well...
 

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