Blog

Written versions of our videos, and other notes on geometry and game development. Most illustrations can be dragged, slid or played with.

Video

Polyhedron Angles Add Up to 720°

Why do the angle defects of every convex polyhedron add up to exactly 720°? A proof with Euler's formula, V − E + F = 2, with interactive illustrations.

Video

How Does a Tesseract Fold?

When folding the cubes of a tesseract, how does the 3D net end up as a 4D tesseract? Considering the rotations we know more carefully, with interactive illustrations you can fold yourself.

Drawing a Catenary

How to draw a string hanging between two points of any height when only the endpoints and the length of the string are known: the catenary, worked out step by step.