Members of a coaxal system satisfy
 |
for values of 
.
Picking 
then gives the two circles
 |
of zero radius, known as point circles. The two point circles 
,
real or imaginary, are called the limiting points
of the coaxal system.
Point Circle
See also
Coaxal System, Limiting PointExplore with Wolfram|Alpha
References
Durell, C. V. Modern Geometry: The Straight Line and Circle. London: Macmillan, p. 123, 1928.Referenced on Wolfram|Alpha
Point CircleCite this as:
Weisstein, Eric W. "Point Circle." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/PointCircle.html