Don't you think this is too easy? Fitzpatrick has this numbered 276 in one of his books online: http://farside.ph.utexas.edu/teaching/336k/Newtonhtml/node43.html But it doesn't take triple-first class honors, or even a degree from Cambridge to "shew" ( this usage is anachronistic ) something so simple about an ellipse. How about the following: Factor[With[{radx = 1/(1 + x Cos[z])}, Subtract[ Dot[D[radx, {x, #}] & /@ {0, 1}, {x, (x - 1) (x + 1)}], D[Sin[z] radx, z]]]] /. Cos[z]^2 -> 1 - Sin[z]^2 Out[]=0. Maybe I'm wrong, I don't know. Is this definition too circular for you? Or perhaps its too elliptical? --Brad On Sat, Dec 14, 2019 at 10:07 AM Bill Gosper <billgosper@gmail.com> wrote:

is an ellipse with focus at the origin. —rwg _______________________________________________ math-fun mailing list math-fun@mailman.xmission.com https://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun