Bend
The bend of a circle C mutually tangent to three other circles is defined as the signed curvature of C. If the contacts are all external, the signs of the bends of all four circles are taken as positive, whereas if one circle surrounds the other three, the sign of this circle is taken as negative (Coxeter 1969). Bends can also be defined for spheres.
See also
Curvature, Descartes Circle Theorem, Soddy CirclesExplore with Wolfram|Alpha
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References
Coxeter, H. S. M. Introduction to Geometry, 2nd ed. New York: Wiley, pp. 13-14, 1969.Referenced on Wolfram|Alpha
BendCite this as:
Weisstein, Eric W. "Bend." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/Bend.html