Math Problem Statement

Find the 8th term of a geometric sequence whose 3rd term is 27 and the common ratio is 3.

Solution

To find the 8th term of a geometric sequence, we use the formula for the nn-th term of a geometric sequence:

an=a1rn1a_n = a_1 \cdot r^{n-1}

Where:

  • ana_n is the nn-th term.
  • a1a_1 is the first term.
  • rr is the common ratio.
  • nn is the term position.

Step 1: Identify the given information

  • The 3rd term (a3a_3) is 27.
  • The common ratio (rr) is 3.

Step 2: Find the first term (a1a_1)

The formula for the 3rd term is: a3=a1r31a_3 = a_1 \cdot r^{3-1}

Substitute a3=27a_3 = 27 and r=3r = 3: 27=a13227 = a_1 \cdot 3^2

Simplify: 27=a1927 = a_1 \cdot 9

Solve for a1a_1: a1=279=3a_1 = \frac{27}{9} = 3

Step 3: Find the 8th term (a8a_8)

Now use the formula for the 8th term: a8=a1r81a_8 = a_1 \cdot r^{8-1}

Substitute a1=3a_1 = 3, r=3r = 3, and n=8n = 8: a8=337a_8 = 3 \cdot 3^{7}

Simplify: a8=32187=6561a_8 = 3 \cdot 2187 = 6561

Final Answer:

The 8th term of the sequence is: 6561\boxed{6561}

Would you like further details or explanations?


Related Questions:

  1. What is the formula for the sum of the first nn terms in a geometric sequence?
  2. How does the common ratio affect the growth of a geometric sequence?
  3. What is the 10th term of this sequence?
  4. How do you determine if a sequence is arithmetic or geometric?
  5. Can you derive the general term formula for a geometric sequence?

Tip: When working with geometric sequences, always verify the common ratio and calculate step-by-step to avoid compounding errors.

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Math Problem Analysis

Mathematical Concepts

Geometric Sequences
Exponents

Formulas

General formula for the nth term of a geometric sequence: an = a1 * r^(n-1)

Theorems

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Suitable Grade Level

Grades 8-10