College

A sequence is defined by the recursive function [tex]$f(n+1)=\frac{1}{3} f(n)$[/tex]. If [tex]$f(3)=9$[/tex], what is [tex][tex]$f(1)$[/tex][/tex]?

A. 1
B. 3
C. 27
D. 81

Answer :

To solve the problem, we need to find [tex]\( f(1) \)[/tex] given the recursive sequence formula [tex]\( f(n+1) = \frac{1}{3}f(n) \)[/tex] and the fact that [tex]\( f(3) = 9 \)[/tex].

Let's work through the problem step-by-step:

1. Start with [tex]\( f(3) \)[/tex]:
We are given that [tex]\( f(3) = 9 \)[/tex].

2. Find [tex]\( f(2) \)[/tex]:
The recursive formula is [tex]\( f(n+1) = \frac{1}{3}f(n) \)[/tex]. To find the previous term [tex]\( f(2) \)[/tex], we need to reverse this operation.
So, multiply by 3:
[tex]\[
f(2) = 3 \times f(3) = 3 \times 9 = 27
\][/tex]

3. Find [tex]\( f(1) \)[/tex]:
Similarly, use the same process to find [tex]\( f(1) \)[/tex] from [tex]\( f(2) \)[/tex]:
[tex]\[
f(1) = 3 \times f(2) = 3 \times 27 = 81
\][/tex]

Therefore, the value of [tex]\( f(1) \)[/tex] is 81.