Answer
$y=-x^2+9$
Work Step by Step
The graph shows that the zeros of the function are $-3$ and $3$. This means that the function contains the factors $x+3$ and $x-3$.
The parabola opens downward so the function is:
$y=-(x+3)(x-3)\\
y=-(x^2-3x+3x-9)\\
y=-(x^2-9)\\
y=-x^2+9$
(The graph does not show point other than its zeros that have integral $y$-value so we have to assume that $a=-1$).
