Prove the set of irrational numbers is uncountable.

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SUMMARY

The set of irrational numbers is proven to be uncountable by leveraging the established facts that the set of rational numbers, denoted as , is countable, while the set of real numbers, , is uncountable. By demonstrating that if both rational and irrational numbers were countable, it would contradict the uncountability of real numbers, one can conclude that the set of irrational numbers is indeed uncountable. This proof utilizes the properties of set theory and cardinality.

PREREQUISITES
  • Understanding of set theory concepts, particularly countability and uncountability.
  • Familiarity with the definitions of rational numbers () and real numbers ().
  • Knowledge of basic logic and proof techniques, including proof by contradiction.
  • Basic understanding of cardinality and how it applies to different sets.
NEXT STEPS
  • Study the properties of countable and uncountable sets in more detail.
  • Learn about Cantor's diagonal argument and its implications for set theory.
  • Explore the implications of cardinality in real analysis and topology.
  • Investigate other proofs of uncountability, such as the uncountability of the power set.
USEFUL FOR

Mathematics students, educators, and anyone interested in advanced set theory and proofs regarding the nature of numbers.

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Homework Statement


Prove the set of irrational numbers is uncountable.


Homework Equations





The Attempt at a Solution


We proved that the set [0,1] is uncountable, but I'm not sure how to do it for the irrational numbers.
 
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You have probably shown:
1) The set \mathbb{Q} of rational numbers is countable.
2) The set \mathbb{R} of real numbers is uncountable.
3) The union of two countable sets is countable.
Now if both the set of rational numbers and the set of irrational numbers were countable would you be able to get a contradiction using fact 2 and 3? You should be able to use this contradiction to show that the set of irrational numbers must be uncountable.
 

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