## Soddy's formulaIf four circles A, B, C,
and D, of radii r_{1}, r_{2},
r_{3}, and r_{4}, are drawn so that they
do not overlap but each touches the other three, and if we let b_{1}
= 1/r_{1}, etc., thenb_{1} + b_{2} + b_{3}
+ b_{4})^{2} = 2(b_{1}^{2}
+ b_{2}^{2} + b_{3}^{2}
+ b_{4}^{2}).
## Related category• GEOMETRY | |||||

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