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## Main Question or Discussion Point

Actually, this is just a plain old geometry problem, really - no special tricks or anything. It just has a very nice solution, which someone showed me years ago (I take no credit).

There are probably plenty of ugly ways to do this; the point here is

**Can you prove that the intersection of a right circular cylinder and a plane is an ellipse? (Assume the general case of an oblique intersection.)**There are probably plenty of ugly ways to do this; the point here is

*elegance*!