Are the interiors of the subsets Z and Q in R open sets?

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SUMMARY

The discussion focuses on determining whether the interiors of the subsets of real numbers, specifically the integers (Z) and the rationals (Q), are open sets within the standard open-ball topology on the real line. It is established that neither Z nor Q contains any interior points because any open interval around a point in these sets will invariably include points from outside the set. Consequently, the interiors of both Z and Q are empty sets, confirming that they are not open sets in the context of real analysis.

PREREQUISITES
  • Understanding of real analysis concepts, particularly open sets and interior points.
  • Familiarity with the standard open-ball topology on the real line.
  • Knowledge of the properties of rational and integer subsets of real numbers.
  • Basic comprehension of boundary points in set theory.
NEXT STEPS
  • Study the definition and properties of open sets in topology.
  • Learn about the concept of closure and limit points in real analysis.
  • Explore the differences between countable and uncountable sets, particularly in relation to Q and R.
  • Investigate the implications of the Heine-Borel theorem on compact sets in Euclidean spaces.
USEFUL FOR

Students and professionals in mathematics, particularly those studying real analysis, topology, or set theory, will benefit from this discussion.

Piglet1024
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I have to describe the interior of the subsets of R: Z,Q.

I don't understand how to tell if these certain subsets are open or how to tell what the interior is, can someone please explain
 
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Are you working with the standard open-ball topology on the real line?

If so, then a point [itex]p \in S \subset \mathbb{R}[/itex] is an interior point of S if for some [itex]\epsilon >0[/itex], the open interval [itex](p-\epsilon, p+\epsilon)[/itex] lies completely inside. In other words, a point is an interior point if it lies in the set and is not a boundary point of the set.

For example, 2 is an interior point of [1,4], but 1 is not an interior point (on the boundary) and neither is 0 (not in the set).

What happens when you draw a small open interval around a rational number? Will that interval lie completely inside the rational numbers, or does it contain an irrational number?
 

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