Please subscribe to the official Codeforces channel in Telegram via the link https://t.me/codeforces_official. ×

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'