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]f(1)[/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 relationship for the sequence:

[tex]\( f(n+1) = \frac{1}{3} f(n) \)[/tex], with the additional information that [tex]\( f(3) = 9 \)[/tex].

Let's work through it step-by-step:

1. Find [tex]\( f(2) \)[/tex]:
- We know that [tex]\( f(3) = \frac{1}{3} f(2) \)[/tex].
- Since [tex]\( f(3) = 9 \)[/tex], we can set up the equation:
[tex]\[
f(3) = \frac{1}{3} f(2)
\][/tex]
[tex]\[
9 = \frac{1}{3} f(2)
\][/tex]
- To find [tex]\( f(2) \)[/tex], multiply both sides by 3:
[tex]\[
f(2) = 9 \times 3 = 27
\][/tex]

2. Find [tex]\( f(1) \)[/tex]:
- Similarly, from the recursive relationship, [tex]\( f(2) = \frac{1}{3} f(1) \)[/tex].
- We found that [tex]\( f(2) = 27 \)[/tex], so:
[tex]\[
f(2) = \frac{1}{3} f(1)
\][/tex]
[tex]\[
27 = \frac{1}{3} f(1)
\][/tex]
- To find [tex]\( f(1) \)[/tex], multiply both sides by 3:
[tex]\[
f(1) = 27 \times 3 = 81
\][/tex]

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