Sorry, it's 'Differential Equations'. Tried quite a few times and nothing happens except the download link returned to 'ready to download' (highlighted) again without error or message.
It' s strange because 'Trigonometry' downloaded but the file I got was mfg.pdf — Modeling Functions and Graphs. So I don't know what's going on. I can only assume that there's some mixup in their files upload.
If you get it to work then signal as such and I'll try again. Good luck.
There are three linked resources under Differential Equations. All the PDFs (or the most recent if there were multiple) from each downloaded just fine for me.
For Trigonometry check the page again. The page it links to (for the one simply titled "Trigonometry" author Katherine Yoshiwara) there are multiple books available. The second book on that page is Trigonometry. Modeling, Functions, and Graphs is the first book, just below it is Trigonometry: https://github.com/byoshiwara/trig/blob/master/trig.pdf.
It' s strange because 'Trigonometry' downloaded but the file I got was mfg.pdf — Modeling Functions and Graphs. So I don't know what's going on. I can only assume that there's some mixup in their files upload.
If you get it to work then signal as such and I'll try again. Good luck.