Equality of a Segment and an Arc in Archimedes's Spiral

This Demonstration illustrates Proposition 20 of Archimedes's work On Spirals.
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 .


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[1] T. L. Heath (ed.), The Works of Archimedes, New York: Dover Publications, 2002.
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