Eight Ninths and the Geometry of A4 Paper - Universal Hyperbolic Geometry

Explore the fascinating geometry of A4 paper and its connection to the spread of 8/9 in this 25-minute video lecture from the Universal Hyperbolic Geometry series. Discover the mathematical properties of the A series paper sizes, including the ISO standard A4 used worldwide. Learn how to apply Rational Trigonometry to analyze A4 paper dimensions and understand why an A4 sheet cannot be realized in A². Gain insights into the relationship between paper geometry and the regular tetrahedron, and see how viewing a cube from a specific perspective explains this intriguing mathematical coincidence.

Introduction
"The A series" of paper sizes
The defining property of the A sizes
Calculations with Rational trig on A4 paper
An A4 sheet is not realizable in A²