Question

find the zeros of y=x^2-4x-9 by completing the square

Answer 1

$x^2-4x-9=0\\ x^2-4x+4-13=0\\ (x-2)^2=13\\ x-2=-\sqrt{13} \vee x-2=\sqrt{13}\\ x=2-\sqrt{13} \vee x=2+\sqrt{13}$