Citerar Lars Ahlfors,
Complex Analysis, § 3.5.
Families of Circles.
Consider a linear transformation of the form
w = k·(z-a)/(z-b).
Here z = a corresponds to w = 0 and z = 0 to w = ∞. It follows that the straight lines through the origin of the w-plane are images of the circles through a and b. On the other hand, the concentric circles about the origin, |w| = ρ, correspond to circles with the equation
|(z-a)/(z-b)| = ρ.
These are the
circles of Apollonius with limit points a and b. By their equation they are the loci of points whose distances from a and b have a constant ratio.
Kan någon vänlig själ rita en bild för att illustrera det sagda?