If two points and are Inverse with respect to a Circle (the Inversion Circle), then the straight line through which is Perpendicular to the line of the points is called the Polar of the with respect to the Circle, and is called the pole of the Polar.

**References**

Dörrie, H. *100 Great Problems of Elementary Mathematics: Their History and Solutions.* New York: Dover, p. 157, 1965.

Johnson, R. A. *Modern Geometry: An Elementary Treatise on the Geometry of the Triangle and the Circle.* Boston, MA:
Houghton Mifflin, pp. 100-106, 1929.

© 1996-9

1999-05-25