Is sqrt(5) Rational? Understanding the Proof by Contradiction

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Discussion Overview

The discussion revolves around the rationality of square roots, specifically focusing on whether sqrt(5) and sqrt(6) are rational or irrational. Participants explore various proof techniques, including proof by contradiction, and engage in clarifying and challenging each other's arguments. The scope includes theoretical proofs and mathematical reasoning.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant outlines a proof by contradiction to show that sqrt(5) is irrational, relying on the properties of prime numbers.
  • Another participant presents a similar argument for sqrt(6), but their proof is challenged for inconsistencies in reasoning and mathematical steps.
  • A later reply suggests that sqrt(n) is irrational for any positive integer n that is not a perfect square, but this claim is met with questions about the clarity of the assumptions made.
  • Some participants propose a theorem stating that the square root of a product of different prime numbers is irrational, though this is critiqued for being overly simplistic and not universally applicable.
  • Concerns are raised about the validity of certain proofs and the need for more rigorous justification of claims regarding the irrationality of square roots.

Areas of Agreement / Disagreement

Participants express differing views on the validity of various proofs and the assumptions underlying them. There is no consensus on the best approach to proving the irrationality of square roots, and several competing models and arguments are presented.

Contextual Notes

Some arguments rely on specific properties of prime numbers and the uniqueness of prime factorization, while others question the applicability of these properties to all integers. The discussion highlights the complexity of establishing proofs in number theory.

Who May Find This Useful

Readers interested in number theory, mathematical proofs, and the properties of irrational numbers may find this discussion relevant.

  • #61
here's another explanation of gibz's proof which is actually also my favorite: if sqrt(n) = a/b is in lowest form, then n = a^2/b^2 is also in lowest form, but lowest form is unique and n/1 is a lowest form for n, so b^2 = 1 and a^2 = n. i.e. if sqrt(n) is rational, then sqrt(n) is an integer.
 
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