Puzzles with beautiful solutions - Why slicing a cone gives an ellipse (beautiful proof)

Dandelin spheres, conic sections, and a view of genius in math. Help fund future projects: https://www.patreon.com/3blue1brown An equally valuable form of support is to simply share some of the videos. Special thanks to these supporters: http://3b1b.co/dandelin-thanks Home page: https://www.3blue1brown.com Thoughts on the recent change to be sponsor-free: https://www.patreon.com/posts/going-sponsor-19586800 Video on Feynman's lost lecture: https://youtu.be/xdIjYBtnvZU 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: http://3b1b.co/store The 3d animations in the video were done using Grapher, while 2d animations were done using https://github.com/3b1b/manim 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 icon in the video and go to subtitles/cc, then "add subtitles/cc". I really appreciate those who do this, as it helps make the lessons accessible to more people. Music by Vincent Rubinetti: https://vincerubinetti.bandcamp.com/album/the-music-of-3blue1brown Thanks to these viewers for their contributions to translations Hebrew: Omer Tuchfeld ------------------ 3blue1brown is a channel about animating math, in all senses of the word animate. And you know the drill with YouTube, if you want to stay posted on new videos, subscribe: http://3b1b.co/subscribe Various social media stuffs: Website: https://www.3blue1brown.com Twitter: https://twitter.com/3blue1brown Reddit: https://www.reddit.com/r/3blue1brown Instagram: https://www.instagram.com/3blue1brown_animations/ Patreon: https://patreon.com/3blue1brown Facebook: https://www.facebook.com/3blue1brown