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Easy geometry: Radius of pentagon is (xcsc36)/2

Source:

May 9, 2012
geometrycircumcircletrigonometrycomplex numbers

Problem Statement

Show that the vertices of a regular pentagon are concyclic. If the length of each side of the pentagon is xx, show that the radius of the circumcircle is x2sin⁡36∘\frac{x}{2\sin 36^\circ}.
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