Institute of Mathematics, Autonomous National University of Mexico, A.P. 273, Admin. De corers No. 3, 62251 Cuernavaca, MOR, Mexico
Academic Editor: A. Zafer
Copyright © 2010 Jose L. Martinez-Morales. This is an open access article distributed under the
Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Some real functions on the plane can be expressed as a linear combination of powers of distances to certain points.