for values of "r" close to zero, the corresponding circle is close to "c", while for values of "r" close to ∞, the corresponding circle is close to "d"; for the intermediate value "r" = 1, the circle degenerates to a line, the perpendicular bisector of "cd". the equation defining these circles as a locus can be generalized to define the fermat–apollonius circles of larger sets of weighted points.