Why slicing a cone gives an ellipse (beautiful proof)

Dandelin spheres, conic sections, and a view of genius in math. Help fund future projects: An equally valuable form of support is to simply share some of the videos. Special thanks to these supporters: Home page: Thoughts on the recent change to be sponsor-free: Video on Feynman's lost lecture: I originally saw the proof of this video when I was reading Paul Lockhart's “Measurement“, which I highly recommend to all math learners, young and old. New shirts/mugs available: The 3d animations in the video were done using Grapher, while 2d animations were done using If you want to contribute translated subtitles or to help review those that have already been made by others and need approval, you can click the gear ic