Pentagon
In geometry, a pentagon is a polygon with 5 sides. Each angle of a regular pentagon is 
. The sum of the internal angles of any pentagon is 
.
Construction
It is possible to construct a regular pentagon with compass and straightedge:
http://img164.imageshack.us/img164/1296/pentagonconstructiongt4.png
1. Draw circle 
(red).
2. Draw diameter 
and construct a perpendicular radius through .
3. Construct the midpoint of 
, and label it 
.
4. Draw 
(green).
5. Construct the angle bisector of 
, and label its intersection with as 
(pink).
6. Construct a perpendicular to at .
7. Adjust your compass to length 
, and mark off points 
, 
and 
on circle .
8. 
is a regular pentagon.
See also
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