(inglés) : Descartes' circle theorem
Soddy's formulaDefinición Nivel 4
If we draw four circles A, B, C, D so that they do not overlap but each touches the other three, and if we call the radii of the circles r1, r2, r3, r4, and let b1=1/r1, etc, then ( b1 + b2 + b3 + b4 ) 2 = 2 ( b1 2 + b2 2 + b3 2 + b4 2 ).


Financiado por: Socrates Minerva UE, HeyMath!, Cambridge University Press