State and prove a natural generalization

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SUMMARY

The discussion centers on generalizing the Arithmetic-Geometric (AG) Inequality, specifically the case for three positive real numbers, x1, x2, and x3, where x1/x2 + x2/x3 + x3/x1 ≥ 3. Participants explore extending this to four positive real numbers, proposing the inequality x1/x2 + x2/x3 + x3/x4 + x4/x1 ≥ 4. The consensus is that the general form of the inequality can be expressed as (x1 + x2 + ... + xn)/n ≥ √[n]{x1x2...xn}, with suggestions to use proof by induction for validation.

PREREQUISITES
  • Understanding of the Arithmetic-Geometric Mean Inequality
  • Familiarity with mathematical proof techniques, including induction
  • Knowledge of inequalities involving positive real numbers
  • Basic algebraic manipulation skills
NEXT STEPS
  • Study the proof of the Arithmetic-Geometric Mean Inequality
  • Learn about mathematical induction and its applications in proofs
  • Explore generalizations of inequalities in real analysis
  • Investigate other forms of inequalities involving multiple variables
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Mathematicians, students studying real analysis, educators teaching inequalities, and anyone interested in advanced mathematical proofs and generalizations.

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Homework Statement


State and prove a natural generalization of "prove that for any three positive real numbers x1, x2, x3, x1/x2 + x2/x3 + x3/x1 \geq 3.


Homework Equations


AG Inequality is used in subproof (x1/x2 + x2/x3 + x3/x1 \geq 3)


The Attempt at a Solution


I don't know what the book means exactly by a "natural generalization". Does it want me to prove the original AG Inequality or relate it somehow to this specific instance of the AG Inequality?
 
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What's special about the statement being true for 3 numbers? Is it true that for any 4 positive real numbers x_1, x_2, x_3, x_4
<br /> \frac{x_1}{x_2}+\frac{x_2}{x_3}+\frac{x_3}{x_4}+ \frac{x_4}{x_1} \geq 4 \; ?<br />
Can you generalize?
 
So it's asking for a proof of the form (x1+x2+...+xn)/n \geq \sqrt[n]{x<sub>1</sub>x<sub>2</sub>...x<sub>n</sub>} . So, I should prove the Arithmetic-Geometric Mean Inequality?
 
Last edited:
major_maths said:
So it's asking for a proof of the form (x1+x2+...+xn)/n \geq \sqrt[n]{x<sub>1</sub>x<sub>2</sub>...x<sub>n</sub>} . So, I should prove the Arithmetic-Geometric Mean Inequality?

If by "of the form," you mean for n positive real numbers, then yes. I'm guessing the same trick you used for the n=3 case will work in general. If not, proof by induction might work.
 

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