I dropped off at about 70%. For me, it was a few things 1) Too much intro material - The explanation of what a root is was too long. By the time I got to the

I dropped off at about 70%. For me, it was a few things 1) Too much intro material - The explanation of what a root is was too long. By the time I got to the start of the derivation, my attention span was already running out, due to: 2) Too much tedious algebra - I felt annoyed that I needed to do a bunch of basic arithmetic to advance to the next section. 3) Complicated derivation - Like another commenter mentioned, I think the completing the square method would have been shorter and easier than this method.