Eight ninths and the geometry of A4 paper | Universal Hyperbolic Geometry 46 | NJ Wildberger

The geometry of the regular tetrahedron centres around the spread of 8/9. Here we look at the A series of paper sizes, including the A4 letter paper that is the ISO standard used in almost all of the world outside North America (where 8.5″ x 11″ is the standard).

Curiously the shape of the A4 paper has some rather interesting mathematical properties, and the spread of 8/9 plays also a central role. By looking at a cube in the right way, we will explain this seeming coincidence.

Throughout we adopt the modern powerful point of view of Rational Trigonometry: giving us a lot more control and insight into the geometry of the world around us!

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