A very nice, gentle explanation of “envelopes” and their connection to string art (and partial derivatives).
When I was a kid I used to make this sketch: connect (1,0) to (0,10), (2,0) to (0,9), etc. I thought it was cool that these straight lines had a curved boundary. Now I know that this curve is called the *envelope* of the family of lines. What is this curve? 1/7