Multiple angles.Chebychef

http://www.trans4mind.com/personal_development/mathematics/trigonometry/multipleAngles.htm
http://www.trans4mind.com/personal_development/mathematics/trigonometry/multipleAnglesSine.htm
http://www.trans4mind.com/personal_development/mathematics/trigonometry/multipleAnglesTangent.htm

http://mathworld.wolfram.com/TrigonometryAnglesPi13.html

http://en.wikipedia.org/wiki/Exact_trigonometric_constants (poligonos construibles)