Hexagrammum Mysticum 10 | A quick primer on cross ratios and the anharmonic group | Wild Egg Maths

Описание: The cross ratios is a fundamental concept both in affine geometry and projective geometry. Here we give a quick primer, noting some common pitfalls that even advanced geometry texts succumb to, nd introduce the associated anharmonic group, which is a manifestation of the symmetric group S_3 in the form of Mobius transformations which describe all possible cross ratios formed by four collinear points.

Along the way we verify our remarkable new cubic identity formed by a kind of Pappus duality.

The Playlist for the entire series is called Hexagrammum Mysticum and is available to Members of the Wild Egg Maths channel. Please consider joining to get access to dozens of additional videos!

Video Contents:
00:00 Towards Pappus theorem
00:35 A quick primer on the cross ratio
03:57 Definition of cross ratio
08:45 Actual example of a cross ratio
14:37 The anharmonic group


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