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 :

Sure, let's solve this step by step.

We are given the recursive function:
[tex]\[ f(n+1) = \frac{1}{3} f(n) \][/tex]

And we know a specific value:
[tex]\[ f(3) = 9 \][/tex]

We need to determine the value of [tex]\( f(1) \)[/tex].

First, let's find [tex]\( f(2) \)[/tex] using the recursive function. We know:
[tex]\[ f(3) = \frac{1}{3} f(2) \][/tex]
Rearranging this to solve for [tex]\( f(2) \)[/tex]:
[tex]\[ f(2) = 3 \times f(3) \][/tex]
Since [tex]\( f(3) = 9 \)[/tex]:
[tex]\[ f(2) = 3 \times 9 = 27 \][/tex]

Next, let's find [tex]\( f(1) \)[/tex]:
[tex]\[ f(2) = \frac{1}{3} f(1) \][/tex]
Rearranging this to solve for [tex]\( f(1) \)[/tex]:
[tex]\[ f(1) = 3 \times f(2) \][/tex]
Since [tex]\( f(2) = 27 \)[/tex]:
[tex]\[ f(1) = 3 \times 27 = 81 \][/tex]

So, the value of [tex]\( f(1) \)[/tex] is:
[tex]\[ \boxed{81} \][/tex]