Hallo everyone,
Do you know any simple formulas that are often unknown to many? For me, some can be mentioned are
Euler characteristic
2-Ear Theorem
Pigeonhole
Fermat
Handshaking theorem
incenter formula of a triangle
harmonic series sum
pick theorem
Shoelace Formula
McNugget theorem
Caley Formula
... And what about you? Can you share some?
Thank you.