Ellipses have multiple definitions, how are these the same?
A link to the full video is at the bottom of the screen.
Or, for reference: • Why slicing a cone gives an ellipse (...
The full video this comes from proves why slicing a cone gives the same shape as the two-thumbtacks-and-string construction, which is beautiful.
Editing from long-form to short by Dawid Kołodziej