Burchard von Zollern[?] was born before 1025 and died in 1061.
Burchard's son was Friedrich von Zollern[?], born before 1055, died 1114/15 .
... 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, ...