Math 2.0

Sequences, series, summability Series: basic notions Theorem

Leibniz formula for pi

Builds on Alternating series testpi

Statement

The series ∑n=0∞(−1)n2n+1\sum_{n=0}^{\infty} \frac{(-1)^n}{2n + 1} converges, and 1−13+15−17+⋯=π4.1 - \frac{1}{3} + \frac{1}{5} - \frac{1}{7} + \cdots = \frac{\pi}{4}.

Remarks

The series converges by the alternating series test. Its value comes from the power series of arctangent at x=1x = 1, since arctan⁡1=π/4\arctan 1 = \pi/4. The convergence is very slow. The error after the terms up to n=Nn = N is at most 1/(2N+3)1/(2N + 3). Mathlib states it as a limit of partial sums, in Real.tendsto_sum_pi_div_four.

History

Madhava of Sangamagrama or his school found the series in the 14th or 15th century. James Gregory found it again in 1671, and Leibniz in 1673.

Reading path

To understand this page from the ground up, read these 59 pages in order. The foundations come first.

  1. Limit point of a set definition
  2. Local maximum definition
  3. Sequence definition
  4. Limit of a function definition
  5. Local minimum definition
  6. Real sequence definition
  7. Subsequence definition
  8. Continuity at a point definition
  9. Derivative definition
  10. Bounded sequence definition
  11. Cauchy sequence definition
  12. Geometric sequence definition
  13. Limit of a sequence definition
  14. Monotone sequence definition
  15. Series definition
  16. Continuous function definition
  17. Fermat's theorem on stationary points statement
  18. Limit superior definition
  19. Cauchy sequences are bounded statement
  20. Sum of a finite geometric series statement
  21. Monotone convergence theorem for sequences statement
  22. Every sequence has a monotone subsequence statement
  23. Convergent sequence definition
  24. Pointwise convergence definition
  25. Squeeze theorem statement
  26. Alternating series definition
  27. Partial sum definition
  28. Power series definition
  29. Intermediate value theorem statement
  30. Bolzano–Weierstrass theorem statement
  31. The sequence r^n tends to zero for |r| < 1 example
  32. Alternating series test statement
  33. Radius of convergence definition
  34. Uniform convergence definition
  35. Convergent series definition
  36. Sine and cosine definition
  37. Boundedness theorem statement
  38. Cauchy criterion for sequences statement
  39. Uniform convergence on a set definition
  40. Absolute convergence definition
  41. Series of functions definition
  42. A series of nonnegative terms converges iff its partial sums are bounded statement
  43. Sum of a series definition
  44. Extreme value theorem statement
  45. Uniformly Cauchy sequence of functions definition
  46. Geometric series example
  47. Comparison test statement
  48. Rolle's theorem statement
  49. Root test statement
  50. Weierstrass M-test statement
  51. Mean value theorem statement
  52. Cauchy–Hadamard theorem statement
  53. Power series converge uniformly on smaller discs inside the radius of convergence statement
  54. Uniform convergence of derivatives allows term-by-term differentiation statement
  55. Term-by-term differentiation statement
  56. Power series are differentiable inside the radius of convergence statement
  57. Derivative of cosine statement
  58. pi object
  59. Leibniz formula for pi statement

Where this leads

1 page builds on this one.

Further reading

  1. Web https://en.wikipedia.org/wiki/Leibniz_formula_for_π, lead section
About this page
Tag037FD5NBRT
URIm2://037FD5NBRT
Aliasesmadhava-leibniz-series
Kindstatement, theorem
WritingW1 stated
MSC40A05
StatusThis copy of the site has no build data. Run m2 status 037FD5NBRT.
UsesAlternating series test, pi
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