Trigonometry and its History - 1. right angled triangles

Aiming for enrichment of school mathematics, I tell the history of elementary trig from ancient Greece to India, and back to Europe. We meet a Babylonian spreadsheet all about Pythagoras's theorem, well over 1000 years before Pythagoras. We find that the first trigonometry didn't have right angled triangles at all, but only a circle and a chord. I tell the mysterious story of how sine got its name.

[KipIngram]

Well, it's more sensible for US to measure angles using decimal degrees, since we count in base 10. It made more sense for the Babylonians to do exactly what they did.