Question 1087388
The y-intercept is the point (0,8), which is also the vertex. 
So f(x) = a(x-0)^2 + 8
We know the function passes through the two points (-8,0) and (8,0). Use one of these to find a.
0 = a*8^2 + 8 -> a = -1/8
Thus f(x) = (-1/8)x^2 + 8