Answer: Choice D
f(n) = 4*(3)^(n-1)
f(5) = 324
=======================================================
Explanation:
Look at the y coordinates: {4, 12, 36, 108}
This is a geometric sequence with starting term a = 4 and common ratio r = 3. You start with 4 and multiply by 3 to generate each term
4*3 = 12
12*3 = 36
36*3 = 108
The nth term of the geometric sequence is
f(n) = a*(r)^(n-1)
f(n) = 4*(3)^(n-1)
Now plug in n = 5
f(n) = 4*(3)^(n-1)
f(5) = 4*(3)^(5-1)
f(5) = 4*(3)^(4)
f(5) = 4*81
f(5) = 324
Or you could multiply the last term in {3,12,36,108} by the common ratio 3 to get 108*3 = 324 as the fifth term.
