Thanks wfl, brad klee, etc for all the (resoundingly affirmative) responses. When you all work on such a pure math-y question, do you feel a twinge of irrelevance? I mean, who sections elliptical cones? Dishware from Dong Lai Shun Restaurant in Mountain View: https://s3-media4.fl.yelpcdn.com/bphoto/We4TAw4FEsYATsaBogX9Xw/o.jpg The symmetry of the elongated ellipse from slicing an already elliptical cone is perhaps even more surprising than in the circular conic construction, with no Dandelin spheres to save you. —rwg -------- Original Message -------- Subject: Re: [math-fun] "Solid" geometry Date: 2019-05-20 17:54 From: Dan Asimov <dasimov@earthlink.net> To: math-fun <math-fun@mailman.xmission.com> Reply-To: Dan Asimov <dasimov@earthlink.net>, math-fun <math-fun@mailman.xmission.com> If we apply a linear transformation to the elliptical cone to get a round one, the sectioning plane goes to another plane cutting a conic section, so the inverse transformation shows the answer is Yes, since linear images of conic sections are still conic. —Dan ----- Is a section of an elliptical cone a Conic Section? ----- _______________________________________________