Substituting into vertex form, we can write the equation of the parabola as
[tex]y=a(x-0)^{2}+9\\\\y=ax^{2}+9[/tex]
To find the value of a, we can substitute in the coordinates of another point the graph passes through, such as (3,0).
[tex]0=a(3)^{2}+9\\\\0=9a+9\\\\-9=9a\\\\a=\boxed{-1}[/tex]
