Two equilateral triangles are constructed such that they share a side with a third triangle as shown.

Find the value of the angle coloured red

This problem is from the excellent book Geometry Snacks by and reproduced here with permission. (c) 2017 Ed Southall and Vincent Pantaloni https://www.tarquingroup.com/geometry-snacks.html

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Tracey Peto,

Friday, August 2, 2019

"Hi John, brill web site. However I really have no clue at all about Geometry Snacks which you downloaded from the book. At what level do you think this would be appropriate?

[Transum: Thanks. I think it would be appropriate for A Level, IB students or to really challenge Higher GCSE students.]"

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