Question
Question or the following sequence, give an explicit formula for the \( n \)th term. Do not include " \( a_{n}= \) " in your response. \[ \frac{6}{7},-\frac{36}{13}, \frac{216}{19},-\frac{1296}{25}, \frac{7776}{31}, \ldots \]
Ask by Lynch Rodriquez. in the United States
Mar 19,2025
Upstudy AI Solution
Tutor-Verified Answer
Answer
The \( n \)th term is \( (-1)^{n+1} \times \frac{6^n}{6n+1} \).
Solution
Observe that the numerators of the terms are
\[
6,\ -36,\ 216,\ -1296,\ 7776,\ \dots
\]
These values can be expressed as powers of 6 with alternating signs. In particular, the first term is \( 6^1 \), the second is \(-6^2\), the third is \( 6^3 \), etc. A pattern of alternating signs emerges, which can be captured by the factor \((-1)^{n+1}\) when \( n \) starts at 1. Hence, the numerator is given by
\[
(-1)^{n+1}6^n.
\]
Next, consider the denominators:
\[
7,\ 13,\ 19,\ 25,\ 31,\ \dots
\]
Notice that each successive term increases by 6. Thus, starting from 7, the \( n \)th denominator is
\[
7 + 6(n-1) = 6n + 1.
\]
Combining the two observations, an explicit formula for the \( n \)th term is
\[
(-1)^{n+1}\frac{6^n}{6n+1}.
\]
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The Deep Dive
The \( n \)th term can be expressed as \( (-1)^{n-1} \cdot \frac{6^n}{6n + 1} \). This sequence showcases a fascinating blend of alternating signs and exponential growth, divided by a linear polynomial in the denominator, making it a captivating example of mathematical patterns!