Equality of a Segment and an Arc in Archimedes's Spiral
This Demonstration illustrates Proposition 20 of Archimedes's work On Spirals.[more]
Let be any point on the first turn of the spiral, and let be the intersection of the tangent to the spiral at , with the perpendicular to at . Then .[less]
 T. L. Heath (ed.), The Works of Archimedes, New York: Dover Publications, 2002.