Math Problem Statement

The 1st term of a geometric sequence is 3 and the eighth term is 384. Find the common ratio

Solution

A geometric sequence follows the formula:

an=a1r(n1)a_n = a_1 \cdot r^{(n-1)}

where:

  • ana_n is the nnth term,
  • a1=3a_1 = 3 (given),
  • n=8n = 8,
  • a8=384a_8 = 384,
  • rr is the common ratio.

Step 1: Substitute the known values into the formula

384=3r(81)384 = 3 \cdot r^{(8-1)}

384=3r7384 = 3 \cdot r^7

Step 2: Solve for rr

First, divide both sides by 3:

3843=r7\frac{384}{3} = r^7

128=r7128 = r^7

Now, take the seventh root of both sides:

r=1287r = \sqrt[7]{128}

Since 128=27128 = 2^7, we get:

r=2r = 2

Final Answer:

The common ratio is 2.

Would you like a step-by-step explanation for a different approach or more details?

Here are some related questions for further understanding:

  1. How do you find the sum of a geometric sequence?
  2. What happens if the common ratio is negative?
  3. How do you determine the common ratio if given two non-consecutive terms?
  4. How does the common ratio affect the growth of a geometric sequence?
  5. How can geometric sequences be applied in real-life situations?

Tip: In a geometric sequence, the common ratio remains constant between consecutive terms. Always check by dividing one term by the previous term.

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Math Problem Analysis

Mathematical Concepts

Geometric Sequences
Exponents
Radicals

Formulas

a_n = a_1 * r^(n-1)

Theorems

Geometric Sequence Formula

Suitable Grade Level

Grades 7-9