Math 2.0

Field theory and polynomials Theorem

Impossibility of squaring the circle

Builds on Squaring the circleTranscendence of piThe degree of a constructible number is a power of two

Statement

The number π\sqrt{\pi} is not a constructible number. So the circle cannot be squared with straightedge and compass.

Remarks

The proof: every constructible number is algebraic over ℚ\mathbb{Q}. If π\sqrt{\pi} were constructible, then π=(π)2\pi = (\sqrt{\pi})^2 would be constructible and so algebraic. This contradicts the transcendence of π\pi.

History

The impossibility was proved in 1882, as a consequence of Lindemann's proof that π\pi is transcendental. It had been known for decades that the transcendence of π\pi would imply the impossibility.

Reading path

To understand this page from the ground up, read these 60 pages in order. The foundations come first.

  1. Group concept
  2. Straightedge and compass construction concept
  3. Ring definition
  4. Constructible number definition
  5. Squaring the circle problem
  6. Commutative ring definition
  7. Ideal definition
  8. Polynomial ring definition
  9. Ring homomorphism definition
  10. Subring definition
  11. Unit of a ring definition
  12. Zero divisor definition
  13. Divisibility in a commutative ring definition
  14. Ideal generated by a subset definition
  15. Maximal ideal definition
  16. Two-sided ideal definition
  17. Degree of a polynomial definition
  18. Polynomial evaluation definition
  19. Field definition
  20. Integral domain definition
  21. Kernel of a ring homomorphism definition
  22. Ring isomorphism definition
  23. Principal ideal definition
  24. Quotient ring definition
  25. The only ideals of a field are zero and the whole field statement
  26. Evaluation homomorphism definition
  27. Leading coefficient definition
  28. Root of a polynomial definition
  29. Subfield definition
  30. Irreducible element definition
  31. Euclidean domain definition
  32. Correspondence theorem for rings statement
  33. Principal ideal domain definition
  34. The constructible numbers form a field closed under square roots statement
  35. Monic polynomial definition
  36. Universal property of the quotient ring statement
  37. Irreducible polynomial definition
  38. Degree of a product statement
  39. Field extension definition
  40. R/M is a field iff M is maximal statement
  41. In a PID a nonzero element is irreducible iff it generates a maximal ideal statement
  42. Division algorithm for polynomials statement
  43. Algebraic element definition
  44. R[x] is an integral domain iff R is statement
  45. First isomorphism theorem for rings statement
  46. Intermediate field definition
  47. Degree of a field extension definition
  48. Transcendental element definition
  49. Minimal polynomial of an algebraic element definition
  50. K[x] is a Euclidean domain statement
  51. Field generated by adjoining elements definition
  52. Tower law statement
  53. Transcendence of pi statement
  54. The minimal polynomial divides every polynomial vanishing at the element statement
  55. K[x]/(f) is a field iff f is irreducible statement
  56. Simple extension definition
  57. K(a) is isomorphic to K[x] modulo the minimal polynomial statement
  58. Degree of a simple extension is the degree of the minimal polynomial statement
  59. The degree of a constructible number is a power of two statement
  60. Impossibility of squaring the circle statement

Where this leads

1 page builds on this one.

Further reading

  1. Web https://en.wikipedia.org/wiki/Squaring_the_circle, Impossibility
About this page
Tag0X7CVDE3BG
URIm2://0X7CVDE3BG
Kindstatement, theorem
WritingW0 stub
MSC12F05
StatusThis copy of the site has no build data. Run m2 status 0X7CVDE3BG.
UsesSquaring the circle, Transcendence of pi, The degree of a constructible number is a power of two

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