Answer:
f(x) = -5/81( x^2 -2x - 80)
Explanation:
The zeroes are -8 and 10 so we can write :
f(x) = -a(x - 10)(x + 8)
( negative is because the parabola opens downwards).
The maximum value is at the vertex = 5.
f(x) = -a(x^2 - 2x - 80)
= a[(x - 1)^2 - 1 - 80)
= a(x - 1)^2 - 81a
As the vertex is at f(x) = 5
81a = 5 so a = 5/81
So the equation is
f(x) = -5/81( x^2 -2x - 80)