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Kissing circles. Given three mutually tangent circles (black), there are, in general, two possible answers (red) as to what radius a fourth tangent circle can have. In geometry, Descartes' theorem states that for every four kissing, or mutually tangent, circles, the radii of the circles satisfy a certain quadratic equation. By solving this ...
Tangent lines to circles; Circle packing theorem, the result that every planar graph may be realized by a system of tangent circles; Hexafoil, the shape formed by a ring of six tangent circles; Feuerbach's theorem on the tangency of the nine-point circle of a triangle with its incircle and excircles; Descartes' theorem; Ford circle; Bankoff circle
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Download as PDF; Printable version; In other projects ... Casey's theorem; Circle packing theorem; Clifford's circle theorems; Constant chord theorem; D. Descartes ...
René Descartes gave a formula relating the radii of the solution circles and the given circles, now known as Descartes' theorem. Solving Apollonius' problem iteratively in this case leads to the Apollonian gasket , which is one of the earliest fractals to be described in print, and is important in number theory via Ford circles and the Hardy ...
They are all named for Frederick Soddy, who rediscovered Descartes' theorem on the radii of mutually tangent quadruples of circles. Any triangle has three externally tangent circles centered at its vertices. Two more circles, its Soddy circles, are tangent to the three circles centered at the vertices; their centers are called Soddy centers.
A special case of Descartes' theorem on the sphere has three circles of radius 60° (''k'' = 1/√3, in blue) for which both circles touching all three (in green) have radius 30° (''k'' = √3). Items portrayed in this file
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