Answer:
f(x) = -1/4(x - 0)^2 - 2
Explanation:
vertex form:
f(x) = a(x - h)^2 + k
1) put the vertex in the equation, ( (h, k) is the vertex)
f(x) = a(x - 0)^2 - 2
2) plug in the point (8, -18) to find the value of a
-18 = a(8 - 0)^2 - 2
-18 = a(64) - 2
-16 = a(64)
-16/64 = a
-1/4 = a
3) plug in the value of a into the equation
f(x) = -1/4(x - 0)^2 - 2