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