Math Problem Statement

Which recursive formula can be used to define this sequence for n>1? 2, 6, 18, 54, 162, 486, ...

Solution

The given sequence is: 2,6,18,54,162,486,2, 6, 18, 54, 162, 486, \dots

To find a recursive formula, observe the pattern:

  • 62=3\frac{6}{2} = 3
  • 186=3\frac{18}{6} = 3
  • 5418=3\frac{54}{18} = 3
  • 16254=3\frac{162}{54} = 3
  • 486162=3\frac{486}{162} = 3

This shows that each term is obtained by multiplying the previous term by 3. Therefore, the recursive formula can be expressed as:

an=3an1forn>1a_n = 3 \cdot a_{n-1} \quad \text{for} \quad n > 1

with the initial condition:

a1=2a_1 = 2

Thus, the recursive formula for the sequence is:

an=3an1,wherea1=2a_n = 3 \cdot a_{n-1}, \quad \text{where} \quad a_1 = 2

Would you like a more detailed explanation or have any questions?

Here are 5 related questions to expand on this concept:

  1. How can we generalize a recursive formula for any geometric sequence?
  2. What is the explicit (non-recursive) formula for this sequence?
  3. How do you determine whether a sequence is arithmetic or geometric?
  4. Can you provide an example of a recursive sequence that decreases over time?
  5. What is the sum of the first nn terms in a geometric sequence?

Tip: In geometric sequences, the ratio between consecutive terms (called the common ratio) is constant, which makes finding recursive formulas straightforward.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Sequences
Geometric Sequences
Recursion

Formulas

a_n = 3 * a_(n-1)
a_1 = 2

Theorems

Recursive Definition for Geometric Sequences

Suitable Grade Level

Grades 9-10