Math Problem Statement

Write an explicit formula for a, start subscript, n, end subscripta n ​ , the n, start superscript, th, end superscriptn th term of the sequence 7, comma, 35, comma, 175, comma, point, point, .7,35,175,....

Solution

The given sequence is:

7,35,175,7, 35, 175, \dots

To identify the pattern, we can look at the ratio between consecutive terms:

357=5and17535=5\frac{35}{7} = 5 \quad \text{and} \quad \frac{175}{35} = 5

Since the ratio between consecutive terms is constant, this is a geometric sequence with a common ratio r=5r = 5 and the first term a1=7a_1 = 7.

The general formula for the nn-th term of a geometric sequence is:

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

Substitute a1=7a_1 = 7 and r=5r = 5:

an=75n1a_n = 7 \cdot 5^{n-1}

Thus, the explicit formula for the nn-th term of the sequence is:

an=75n1a_n = 7 \cdot 5^{n-1}

Would you like more details or have any questions?

Here are 5 questions that expand on this concept:

  1. How do you derive the formula for the nn-th term of a geometric sequence?
  2. What is the 6th term in the sequence using the formula an=75n1a_n = 7 \cdot 5^{n-1}?
  3. What happens if the common ratio rr is less than 1 in a geometric sequence?
  4. Can you determine the sum of the first 5 terms of the given sequence?
  5. How does a geometric sequence differ from an arithmetic sequence?

Tip: In a geometric sequence, if the common ratio is greater than 1, the terms grow exponentially.

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Math Problem Analysis

Mathematical Concepts

Geometric Sequences
Patterns
Exponential Growth

Formulas

aₙ = a₁ * r^(n-1)

Theorems

Geometric Sequence Formula

Suitable Grade Level

Grades 9-12