>>16770317
>>16771292
>The letters I'm using are from figure 30, page 52 of the book I linked in my previous post.

Meaning this book:

https://crossworks.holycross.edu/cgi/viewcontent.cgi?article=1062&context=hc_books

Picrel is the relevant part taken from that book.

Also, reading Elements Heath Dover I can see that in proposition IV.1 the text for the proposition doesn't have any references whatsoever, while https://elements.ratherthanpaper.com/4.1 references I.3, http://aleph0.clarku.edu/~djoyce/java/elements/bookIV/propIV1.html references I.3 and IV.Def.7, https://farside.ph.utexas.edu/Books/Euclid/Elements.pdf references I.3 and III.1, and https://youtu.be/ef34vXOzRXw references I.2.

Therefore if you are only reading Elements Heath Dover and nothing else I recommend you supplement it with other sources, both for references which might not be in Dover and also for comparing text and commentary between different materials.

https://archive.org/details/euclid_heath_2nd_ed/2_euclid_heath_2nd_ed
https://elements.ratherthanpaper.com/
http://aleph0.clarku.edu/~djoyce/java/elements/elements.html
https://farside.ph.utexas.edu/Books/Euclid/Elements.pdf
https://www.c82.net/euclid/
https://archive.org/details/elementsofeuclid00eucl
https://www.youtube.com/c/SandyBultena/playlists
https://www.youtube.com/playlist?list=PL2V76rajvC1I2TrbPMRLcTqhdcbha4sDE (only book 1)
https://en.wikipedia.org/wiki/Euclid%27s_Elements#External_links
etc

>>16771292
>Then you could use proposition I.2 to transfer it to the diameter of the circle
I meant to say I.3. Maybe I said I.2 because Sandy Bultena references I.2 in her video on proposition IV.1, which I linked above. But I think she made a mistake. The other three links, ratherthanpaper.com, aleph0.clarku and farside.ph.utexas all reference I.3 and not I.2, and it makes sense when you think about it that it should be I.3. Anyway I think her videos are good despite this mistake.