Envelopes are cool.

Interactive Demos on Desmos:
https://www.desmos.com/calculator/ihm...
https://www.desmos.com/calculator/tho...

Did I get anything wrong? Let me know! I swept over a lot of interesting things here to keep it short!

This was made as part of 3Blue1Brown's Summer of Math Exposition: https://www.3blue1brown.com/blog/some1
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