What is the explicit rule for the nth term of the geometric sequence? 3, 18, 108, 648, 3,888, O an = 3(6") Oan=3(6+¹) O an = 6(3-1) O an=3(6-1)

Calculus: Early Transcendentals
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Author:James Stewart
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Chapter1: Functions And Models
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**Understanding Geometric Sequences**

**Question:**
What is the explicit rule for the nth term of the geometric sequence?

**Given Sequence:**
\[3, 18, 108, 648, 3,888, \ldots\]

**Answer Choices:**

1. \[ a_n = 3(6^n) \]
2. \[ a_n = 3(6^{n+1}) \]
3. \[ a_n = 6(3^{n-1}) \]
4. \[ a_n = 3(6^{n-1}) \]

**Explanation:**

A geometric sequence is a sequence of numbers where each term after the first is found by multiplying the previous term by a constant called the common ratio.

To determine the common ratio (\(r\)), we divide any term by the previous term:

\[ r = \frac{18}{3} = 6 \]
\[ r = \frac{108}{18} = 6 \]
\[ r = \frac{648}{108} = 6 \]

Given that the common ratio is constant (6), we need to find a formula that properly represents this relationship.

To write the explicit formula for the nth term of a geometric sequence, we use the formula:
\[ a_n = a_1 \cdot r^{(n-1)} \]

Where:
- \(a_n\) = the nth term
- \(a_1\) = the first term of the sequence
- \(r\) = the common ratio
- \(n\) = the term number

Here:
- \(a_1 = 3\)
- \(r = 6\)

Plug these values into the formula:
\[ a_n = 3 \cdot 6^{(n-1)} \]

Thus, the correct choice is:
\[ \boxed{a_n = 3(6^{n-1})} \]
Transcribed Image Text:**Understanding Geometric Sequences** **Question:** What is the explicit rule for the nth term of the geometric sequence? **Given Sequence:** \[3, 18, 108, 648, 3,888, \ldots\] **Answer Choices:** 1. \[ a_n = 3(6^n) \] 2. \[ a_n = 3(6^{n+1}) \] 3. \[ a_n = 6(3^{n-1}) \] 4. \[ a_n = 3(6^{n-1}) \] **Explanation:** A geometric sequence is a sequence of numbers where each term after the first is found by multiplying the previous term by a constant called the common ratio. To determine the common ratio (\(r\)), we divide any term by the previous term: \[ r = \frac{18}{3} = 6 \] \[ r = \frac{108}{18} = 6 \] \[ r = \frac{648}{108} = 6 \] Given that the common ratio is constant (6), we need to find a formula that properly represents this relationship. To write the explicit formula for the nth term of a geometric sequence, we use the formula: \[ a_n = a_1 \cdot r^{(n-1)} \] Where: - \(a_n\) = the nth term - \(a_1\) = the first term of the sequence - \(r\) = the common ratio - \(n\) = the term number Here: - \(a_1 = 3\) - \(r = 6\) Plug these values into the formula: \[ a_n = 3 \cdot 6^{(n-1)} \] Thus, the correct choice is: \[ \boxed{a_n = 3(6^{n-1})} \]
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