Answer
One that open upwards:
$y=x^2-9$
One that open downwards:
$y=-x^2+9$
Work Step by Step
Use:
$y=a(x-x_1)(x-x_2)$, where $x_1$ and $x_2$ are the $x$ of the x-intercepts.
$y=a[x-(-3)](x-3)=a(x^2-9)$
One that open upwards ($a\gt0$).
$y=1(x^2-9)=x^2-9$
One that open downwards ($a\lt0$).
$y=-1(x^2-9)=-x^2+9$
