The roots of the parabolic equation is at 4 and -2 according to the graph which means that (x+2) and (x-4) are factors.
So our equation right now is:
f(x)=a(x+2)(x-4)
We can pick a different point to find "a" (1,-18).
-18=a(1+2)(1-4)
-9a=-18
a=2
answer: f(x)=2(x+2)(x-4)
