Connectedness of coordinates with one rational point

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SUMMARY

The collection of all points in R² where at least one coordinate is rational is proven to be path-connected. This conclusion is reached by constructing paths using horizontal and vertical segments, demonstrating that any two points can be connected through a series of straight line segments. For example, moving from (0, √2) to (π, 1/2) can be achieved by first moving vertically to (0, 1/2) and then horizontally to (π, 1/2). This method can be generalized to show path-connectedness for any pair of points in the defined set.

PREREQUISITES
  • Understanding of R² and coordinate systems
  • Familiarity with concepts of connectedness and path-connectedness in topology
  • Basic knowledge of constructing geometric paths
  • Experience with rational and irrational numbers
NEXT STEPS
  • Study the properties of path-connected spaces in topology
  • Explore the implications of connectedness in metric spaces
  • Learn about the role of rational numbers in topology
  • Investigate other examples of connected sets in R²
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Mathematicians, students of topology, and anyone interested in the properties of connectedness in mathematical analysis.

hypermonkey2
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Hi all, i found this problem in a topology book, but it seems to be of an analysis flavour. I'm stumped.

Show that the collection of all points in R^2 such that at least one of the coordinated is rational is connected.

My gut says that it should be path-connected too (thus connected), but I am finding the proof elusive... any thoughts?

cheers
 
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It is path-connected. Try paths consisting of horizontal and vertical segments moving along straight lines. For instance, to move from (0, √2) to (π, 1/2), you could first move along the straight line segment from (0, √2) to (0, 1/2), and then along the straight line segment from (0, 1/2) to (π, 1/2). Now find a way to generalize that line of thought.
 

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