Deliverance by James Dickey (in 2001, named as one of the 100 best English-language novels of the 20th century, as chosen by the editorial board of the Modern Library.)
... x) to the expression to the left of "=", that will make it a perfect square trinomial of the form x2 + 2xy + y2. Since "2xy" in this case is (b/a)x, we must have y = ...