Descartes Complex Circle Theorem - Algebra Window Version
This is a sketch of the setup for proving the Complex Version of Descartes' Circle Theorem.
See http://digitalcommons.plattsburgh.edu/cgi/viewcontent.cgi?article=1000&context=mathematics_facpubs
(Published as Northshield, S. (2014). Complex Descartes Circle Theorem. American Mathematical Monthly, 121 (10), 927-931.)
This is a more flexible version of http://tube.geogebra.org/student/m1294089 which lacks the algebra window.