In geometry, an Archimedean circle is any circle constructed from an arbelos that has the same radius as each of Archimedes' twin circles. If the arbelos is normed such that the diameter of its outer (largest) half circle has a length of 1 and r denotes the radiius of any of the inner half circles, then the radius ρ of such an Archimedean circle is given by
There are over fifty different known ways to construct Archimedean circles.
An Archimedean circle was first constructed by Archimedes in his Book of Lemmas. In his book, he constructed what is now known as Archimedes' twin circles.
If and are the radii of the small semicircles of the arbelos, the radius of an Archimedean circle is equal to
This radius is thus .
The Archimedean circle with center (as in the figure at right) is tangent to the tangents from the centers of the small semicircles to the other small semicircle.
Leon Bankoff constructed other Archimedean circles called Bankoff's triplet circle and Bankoff's quadruplet circle.
In 1978 Thomas Schoch found a dozen more Archimedean circles (the Schoch circles) that have been published in 1998. He also constructed what is known as the Schoch line.
Peter Y. Woo considered the Schoch line, and with it, he was able to create a family of infinitely many Archimedean circles known as the Woo circles.
In the summer of 1998, Frank Power introduced four more Archimedes circles known as Archimedes' quadruplets.
In 1831, Nagata (永田岩三郎遵道) proposed a sangaku problem involving two Archimedean circles, which are denoted by W6 and W7 in [3].
In 1853, Ootoba (大鳥羽源吉守敬) proposed a sangaku problem involving an Archimedean circle.
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In geometry, the twin circles are two special circles associated with an arbelos. An arbelos is determined by three collinear points A, B, and C, and is the curvilinear triangular region between the three semicircles that have AB, BC, and AC as their diameters. If the arbelos is partitioned into two smaller regions by a line segment through the middle point of A, B, and C, perpendicular to line ABC, then each of the two twin circles lies within one of these two regions, tangent to its two semicircular sides and to the splitting segment.
In geometry, an arbelos is a plane region bounded by three semicircles with three apexes such that each corner of each semicircle is shared with one of the others (connected), all on the same side of a straight line (the baseline) that contains their diameters. The earliest known reference to this figure is in Archimedes's Book of Lemmas, where some of its mathematical properties are stated as Propositions 4 through 8. The word arbelos is Greek for 'shoemaker's knife'. The figure is closely related to the Pappus chain.
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