Chapter of Abstract Algebra by Romyar Sharifi, with the same Romyar Sharifi byline; no distinct contributed chapter author is established.
Online text: math.ucla.edu/~sharifi/notes/algebra-ch03.html
Cited passages: §3.9, Theorem 3.9.1 and proof, polynomial division when the leading coefficient is a unit; Proposition 3.9.7 and proof, the factor theorem. No publication date is inferred from the URL.