"Descartes' theorem" . "Descartes's theorem (4 tangent circles)" . "Descartes's theorem" . . "Descartes' theorem#Generalizations" . "Descartes' theorem" . . . . . . . . "Descartes' Circle Equation" . . . . "Descartes's Circle Equation" . "Soddy circles" . "Descartes' circle theorem" .