Math Problem Statement

How do I find the nth term in a geometric sequence?

Solution

The image you've uploaded provides instructions on how to find the nth term in a geometric sequence. Here’s a detailed breakdown:

Geometric Sequences: Finding the nth Term

Formula

The formula for finding the nth term in a geometric sequence is:

an=a1×r(n1)a_n = a_1 \times r^{(n-1)}

  • ana_n: The nth term of the sequence.
  • a1a_1: The first term of the sequence.
  • rr: The common ratio.
  • nn: The term number.

Steps for Finding the nth Term:

  1. Find the Common Ratio (r):

    • Divide any term in the geometric sequence by the term preceding it: r=anan1r = \frac{a_{n}}{a_{n-1}}
  2. Substitute Values into the Formula:

    • Use the values you’ve found to calculate the desired term using the formula an=a1×r(n1)a_n = a_1 \times r^{(n-1)}.

Examples:

  • Example 1:

    • First term a1a_1 = 2
    • Common ratio rr = 3
    • Find the 5th term: a5=2×3(51)=2×34=2×81=162a_5 = 2 \times 3^{(5-1)} = 2 \times 3^4 = 2 \times 81 = 162
  • Example 2:

    • First term a1a_1 = 64
    • Common ratio rr = \frac{1}{2}
    • Find the 7th term: a7=64×(12)(71)=64×(12)6=64×164=1a_7 = 64 \times \left(\frac{1}{2}\right)^{(7-1)} = 64 \times \left(\frac{1}{2}\right)^6 = 64 \times \frac{1}{64} = 1

Additional Questions to Explore:

  1. How do you determine the common ratio if you're given two non-consecutive terms in a geometric sequence?
  2. What happens to the nth term if the common ratio rr is less than 1?
  3. Can a geometric sequence have a common ratio of 0? What would be the implications?
  4. How do you find the sum of the first n terms of a geometric sequence?
  5. How does the geometric sequence formula change if the sequence is decreasing?

Tip: Always ensure that the common ratio is consistent throughout the sequence by checking multiple terms. This will help avoid errors when applying the formula.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Geometric Sequences
Sequences and Series

Formulas

Geometric sequence formula: a_n = a_1 × r^(n-1)
Common ratio formula: r = a_n / a_(n-1)

Theorems

-

Suitable Grade Level

Grades 8-10