On 2018-11-11 17:21, Fred Lunnon wrote:
Sadly, technological progress has relegated our early (and usually laboriously crafted) efforts to museum exhibits --- compare the demo at https://en.wikipedia.org/wiki/Dandelin_spheres
WFL And where might we find a similarly technologically ultraprogressive Wikipedient obsoletion of your laboriously crafted gosper.org/binomial.pdf ? —rwg
On 11/11/18, Bill Gosper <billgosper@gmail.com> wrote:
Eons ago, trying to prove that locus-of-constant-difference is a conic section, I reinvented Dandelin spheres, with a possibly simpler proof that does not refer to their centers nor radii. gosper.org/hyperb.GIF uses instead the lemma that all tangents to a sphere from a point are equally long. The drawing probably needs stereo vision to be convincing. I'm not sure I realized at the time that the spheres could be unequal. —rwg