The bend of a circle 
mutually tangent to three other circles is defined as the signed curvature
of 
. 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.
Bend
See also
Curvature, Descartes Circle Theorem, Soddy CirclesExplore with Wolfram|Alpha
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 Web Resource. https://mathworld.wolfram.com/Bend.html