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!

Screenshot PDFs for my videos are available at the website http://wildegg.com. These give you a concise overview of the contents of each lecture. Great for review, study and summary.

My research papers can be found at my Research Gate page, at https://www.researchgate.net/profile/…. I also have a blog at http://njwildberger.com/, where I will discuss lots of foundational issues, along with other things, and you can check out my webpages at http://web.maths.unsw.edu.au/~norman/. Of course if you want to support all these bold initiatives, become a Patron of this Channel at https://www.patreon.com/njwildberger?… .