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On Wed, Feb 15, 2012 at 4:11 PM, Bill Gosper <billgosper@gmail.com> wrote:

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Neil has just uncovered fq.math.ca/Scanned/6-6/hoggatt.pdf predating my http://mathworld.wolfram.com/SquareDissection.html of a square into ten acute isosceles triangles.

Neil also found in a Gardner book a reference to a Monthly paper (June-July 1962, pp550-552) claiming that *any* obtuse triangle can be cut into eight acute isosceles triangles, implying at most nine for dissecting a right isosceles, in contradiction of my round(tan(69)) solutions assertion.  Has anyone a picture of this dissection? --rwg

Martin Gardner gave the 9 triangle dissection in "The Last Recreations" p253 (but Google books and Amazon wont show me that page) also found the following; Dissecting Triangles into Isosceles Triangles - A high school student paper http://math.ca/crux/v22/n3/page97-100.pdf Jim Loys webpage with some dissections of a square into isosceles triangles with 7 and 6 triangles; http://www.jimloy.com/puzz/iso.htm "Can a square be dissected into a finite number of obtuse, isosceles triangles? (1) Show that a square can be dissected into a finite number of OBTUSE, ISOSCELES triangles. (2) What is the minimum number of OBTUSE, ISOSCELES triangles needed to accomplish this? http://answers.yahoo.com/question/index?qid=20090224164301AAtkOqy - A square dissection with 10 obtuse, isosceles triangles is given. http://i524.photobucket.com/albums/cc321/Krejakovic/10tr.jpg