Inversion


Inversion is a onetoone transformation of the points of the plane (except one point) by means of a given circle (circle of inversion). We shall call this circle C, of radius r and centre q. The center of the circle of inversion (center of inversion) has no image. If the center of the circle of inversion is the origin and the radius is 1 this transformation has a simple formula: In the general case, this mapping is given by: The points on the circle of inversion transform into themselves and each point inside the circle is transformed to a point outside the circle (and viceversa). Each point, its image and the center of the circle of inversion are in the same line. Sometimes we call this transformation as reflection in a circle. Each line through the center of inversion is transformed in the same line. Each line not passing through the center of inversion is transformed in a circle through the center of inversion. The inverse of a circle is a straight line or a circle. It is a line if the circle passes through the center of inversion. The image of a circle not passing through the center of inversion is another circle not passing through the center of inversion. REFERENCES Hilber and CohnVossen  Geometry and the Imagination (pag. 253)  Chelsea Publishing Company
Coxeter  Introduction to Geometry  Wiley and Sons.
Pedoe  Circles, a Mathematical View  Dover
Tristan Needham  Visual Complex Analysis. (pag. 124)  Oxford University Press
Rademacher and Toeplitz  The Enjoyment of Mathematics
Ogilvy  Excursions in Geometry (pag. 24) Oxford University Press
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