Math Problem Statement

The first three terms of a sequence are given: 32, 16, 8. Find the 9th term. Write your answer as a decimal or whole number. Round to the nearest thousandth if necessary.

Solution

The problem asks to find the 9th term of the sequence, where the first three terms are given as:

32,16,8,32, 16, 8, \dots

We can observe that this is a geometric sequence because each term is half of the previous one.

Step-by-Step Solution:

  1. Identify the common ratio:
    To find the common ratio rr, divide the second term by the first term: r=1632=12r = \frac{16}{32} = \frac{1}{2}

  2. Formula for the nn-th term of a geometric sequence:
    The general formula for the nn-th term of a geometric sequence is: an=a1×rn1a_n = a_1 \times r^{n-1} Where:

    • a1a_1 is the first term,
    • rr is the common ratio,
    • nn is the term number.
  3. Substitute the known values:
    In this case:

    • a1=32a_1 = 32,
    • r=12r = \frac{1}{2},
    • n=9n = 9.

    Plug these values into the formula: a9=32×(12)91=32×(12)8a_9 = 32 \times \left(\frac{1}{2}\right)^{9-1} = 32 \times \left(\frac{1}{2}\right)^8

  4. Simplify: (12)8=1256\left(\frac{1}{2}\right)^8 = \frac{1}{256} So: a9=32×1256=32256=18a_9 = 32 \times \frac{1}{256} = \frac{32}{256} = \frac{1}{8}

Therefore, the 9th term is 18\frac{1}{8} or 0.125.


Would you like further details on this?
Here are some related questions for practice:

  1. What is the 10th term of this sequence?
  2. How would you find the sum of the first 9 terms of this geometric sequence?
  3. What happens to the sequence as nn approaches infinity?
  4. Can you write the recursive formula for this geometric sequence?
  5. How would the sequence change if the common ratio was negative?

Tip: Geometric sequences decrease or grow exponentially depending on the common ratio. Always check the ratio carefully!

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Math Problem Analysis

Mathematical Concepts

Sequences
Geometric Sequences

Formulas

a_n = a_1 * r^(n-1)
r = a_2 / a_1

Theorems

Geometric sequence formula

Suitable Grade Level

Grades 7-10