Undergrad Quality of rational approximations

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SUMMARY

The discussion centers on the quality of rational approximations for mathematical constants, specifically π, e, and √2. The approximation 22/7 is highlighted as a strong estimate for π, while 355/113 is noted as even more accurate. In contrast, e is approximated well only by 193/71, and √2 requires 99/70 for a decent approximation. The conversation raises questions about the underlying reasons for these differences, suggesting potential geometrical factors and the influence of continued fractions.

PREREQUISITES
  • Understanding of rational approximations and their significance in mathematics.
  • Familiarity with continued fractions and their applications.
  • Basic knowledge of algebraic numbers and their properties.
  • Awareness of Roth's theorem and its implications for approximation.
NEXT STEPS
  • Research the properties of continued fractions and their role in approximating irrational numbers.
  • Study Roth's theorem and its impact on the approximation of algebraic numbers.
  • Explore the historical work of Freeman Dyson on rational approximations.
  • Investigate the geometrical interpretations of rational approximations in number theory.
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Mathematicians, number theorists, and educators interested in the properties of irrational numbers and their rational approximations.

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22/7 is a very good approximation for π. Sqrt(2) doesn’t do that well until 99/70 and e doesn’t do that well until 193/71. 355/113 is even better.

Is there some reason for this? Perhaps geometrical? Why do the ratios of small integers work better for π than other numbers? Or is it just coincidence? ("Gotta be something...")
 
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The pattern of continued fractions?
 
Sure, but e has one too. What's special, if anythnig, about pi?
 
If you want to keep the denominators of the rationals somewhat small, then algebraic numbers are not well approximated by rationals.
https://en.wikipedia.org/wiki/Roth's_theorem

ps. Interesting that Dyson had worked on these matters.
 
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