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Simple but often unknown theorems/lemmas/formula? Do you know?

Revision en8, by duckladydinh, 2017-11-28 04:39:46

Hallo everyone,

Do you know any simple formulas that are often unknown to many? For me, some can be mentioned are

  • Graph: Euler characteristic, Handshaking theorem, Caley Formula, Kirchhoff's theorem, Kőnig's theorem

  • Polygon: 2-Ear Theorem, incenter formula of a triangle, pick theorem, Shoelace Formula

  • Logic: Pigeonhole

  • Prime: Fermat, Wilson's theorem

  • Number: McNugget theorem

  • Fibonacci: Zeckendorf's theorem

  • Counting: Burnside Lemma, stars and bars

  • Combinatorics Identity: Vandermonde's Identity, Hockey-stick identity

  • Math: Linearity of Expectation

  • Other: harmonic series sum

... And what about you? Can you share some?

Thank you.

History

 
 
 
 
Revisions
 
 
  Rev. Lang. By When Δ Comment
en8 English duckladydinh 2017-11-28 04:39:46 37 Tiny change: 'orem\n\n- ' -> 'orem\n\n- Fibonacci: Zeckendorf's theorem\n\n- '
en7 English duckladydinh 2017-11-28 04:38:34 392 Tiny change: '- Graph:\n- - Euler c' -> '- Graph:\n - Euler c'
en6 English duckladydinh 2017-11-23 08:15:37 24
en5 English duckladydinh 2017-11-23 08:15:14 60
en4 English duckladydinh 2017-11-22 00:22:47 18 Tiny change: 'ce Formula... And wh' -> 'ce Formula, McNugget theorem... And wh'
en3 English duckladydinh 2017-11-22 00:19:13 19 Tiny change: 'ck theorem... And wh' -> 'ck theorem, Shoelace Formula... And wh'
en2 English duckladydinh 2017-11-20 23:11:19 35 Tiny change: 'a triangle... And wh' -> 'a triangle, harmonic series sum, pick theorem... And wh'
en1 English duckladydinh 2017-11-20 20:32:45 344 Initial revision (published)