Eric W. Weisstein, Concise Encyclopedia of Mathematics CD-ROM, Bipolar Coordinates, CD-ROM edition 1.0, May 20, 1999 "Bipolar Coordinates". Archived from the original on December 12, 2007. Retrieved December 9, 2006.
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Eric W. Weisstein, Concise Encyclopedia of Mathematics CD-ROM, Bipolar Coordinates, CD-ROM edition 1.0, May 20, 1999 "Bipolar Coordinates". Archived from the original on December 12, 2007. Retrieved December 9, 2006.