Gene, My post has nothing to do with parallelograms. It simply says any two triangles with the same base and height can be trivially interdissected. So one of them might as well be half a rectangle. --rwg On 2016-02-14 15:31, Eugene Salamin via math-fun wrote:

Bill, I didn't see at all how the animated picture illustrated your post. It would be much more clear if you could present a fixed picture of the parallelogram with a line bisecting it into the two triangles, and a picture of a parallelogram with a line indicating the triangle to be chopped off.

-- Gene

From: Bill Gosper <billgosper@gmail.com> To: math-fun@mailman.xmission.com Sent: Sunday, February 14, 2016 1:33 PM Subject: [math-fun] A=bh/2

Remember when they taught you that the area of a triangle is half the area of the parallelogram you get by gluing two copies together? And the area of the parallelogram is the area of the rectangle you get by chopping a triangle off one end and gluing it on the other? Did anybody complain that this doesn't work for sufficiently skewed parallelograms? Fix: gosper.org/A=f(bh).gif --rwg