. . . . . . In this page, the concepts of orthogonal circles
and inversion geometry will be presented.

should describe orthogonal circles and the inversion circle, and such
things as the angle preservation property etc.

### Orthogonal Circles

### Internet references

From Doctor Math, Orthogonal
Circles

From Mathworld, Orthogonal
Circles, Inversion

From Cut-the-knot, Inversion:
Reflection in a Circle and Inversion
circle

Paul Kunkel's Inversion
Geometry

### Related
pages in this website

Triangle centers,
incircle, excircles, and the nine-point circle -- the nine-point circle is
tangent to the incircle and the three excircles by Feuerbach's Theorem, a fact
that is proved on cut-the-knot using inversion circles.

The webmaster and author of this Math Help site is
Graeme McRae.