Bill T. wrote: << It used to be a standard and well-known geometry fact that given a point and a circle, all lines through the point intersect the circle at two distances that have the same geometric mean = the length of a tangent. This is easy to prove using similar triangles, given the fact that all arcs of circles subtend the same angle as seen from any point on the circle outside the arc. Apply this to the bottom of the wall.
Phrased in this manner, this has to be the Book proof. --Dan P.S. What's this about a Paris fashion show in which at least one designer based their clothing on geometric theories of some American mathematician? More -- but way too little -- at < http://www.nytimes.com/2010/03/06/fashion/06iht-rrick.html >. ________________________________________________________________________________________ "Outside of a dog, a book is man's best friend. Inside of a dog, it's too dark to read." --Groucho Marx