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).(adsbygoogle = window.adsbygoogle || []).push({});

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 iselegance!

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# Geometry puzzle: plane X cylinder = ellipse

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