The tympanum

A regular pentagon with a diagonal and an extended side. What is the top angle of the isosceles triangle?

Scroll down for a solution to this problem.


The angle α is 108°.

Solution by Dr Rick.


The tympanum found in architecture element
Or in an arch or pediment
But not only
Tympanum is also anatomy
And eardrum in biology
Last but not least a handdrum or timpani
Some buildings have it as religious imagery
You can see a lot of examples
As usually
In my small poetry


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