This list exists because I remember reading somewhere (which I can't find right now) that there is a mechanism to track changes to an article to check for vandalism. I am interested in these topics, so I have included them here.
... it a perfect square trinomial of the form x2 + 2xy + y2. Since "2xy" in this case is (b/a)x, we must have y = b/(2a), so we add the square of b/(2a) to both sides, ...