My cotangent identity proof: if α + ß + γ = π then ctg(α/2) + ctg(ß/2) + ctg(γ/2) = ctg(α/2) · ctg(ß/2) · ctg(γ/2)

Interesting puzzle inspired by cizikci Here's my elegant solution

The twelve-pointed star problem by Matilda Spicer My solutions to this regular dodecagon problem:

Regular hexagon. My proof that 5/24 is cyan and that G is midpoint of MD

Regular pentagon. My proof that yellow quadrilaterals have equal areas, ∠LPN=108° and |PL|/|PK|=Golden Ratio

Regular dodecagon. My proof that green triangles are congruent & M is midpoint of KB

Regular pentagon and two congruent squares. This puzzle by Yuri Kazakov allows to build 99° angle

Two regular concentric hexagons. Even though internal hexagon is perfectly aligned, the external one has some peculiar rotation angle.

Proving very beautiful equation: ✨ tgα + 2tg2α + 4tg4α + 8ctg8α = ctgα

d'Ocagne's identity for Fibonacci numbers

Two regular concentric hexagons.

Definite integral

Partitioned regular hexagon

13/70 of right triangle is green

Regular hexagon and right kites. Author of the puzzle is Matilda Spicer

Regular pentagon problem