Answer:
f(n + 1) = 3f(n) with a₁ = 6
Explanation:
The common ratio r of the geometric sequence is
r = 18 ÷ 6 = 3
Thus to obtain the next term in the sequence multiply the previous term by 3
Expressing this as a recursive function then
f(n + 1 ) = 3f(n) with a₁ = 6