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Ch. 10 - Sequences and Infinite Series
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Non è quello che usi tu?Cambia libro di testo
Capitolo 10, Problema 10.2.55

55–70. More sequences
Find the limit of the following sequences or determine that the sequence diverges.


{(−1)ⁿ / 2ⁿ}

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Identify the general term of the sequence, which is given by \(a_n = \frac{(-1)^n}{2^n}\).
Recall that \((-1)^n\) alternates between \(1\) and \(-1\) as \(n\) increases, causing the numerator to alternate signs.
Note that the denominator \$2^n$ grows exponentially as $n$ increases, becoming very large.
Consider the behavior of the absolute value of the terms: \(\left|a_n\right| = \frac{1}{2^n}\), which approaches \(0\) as \(n \to \infty\).
Since the numerator only changes sign but the magnitude approaches zero, conclude that the sequence converges to \(0\).

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Sequence and Limit

A sequence is an ordered list of numbers defined by a specific formula. The limit of a sequence is the value that the terms approach as the index goes to infinity. Understanding how to find limits helps determine if a sequence converges to a finite value or diverges.
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Behavior of Exponential Terms

Exponential terms like 2ⁿ grow rapidly as n increases. When in the denominator, such terms cause the overall fraction to approach zero. Recognizing this behavior is key to evaluating limits involving exponential expressions.
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Alternating Sequences

An alternating sequence changes sign with each term, often represented by (−1)ⁿ. While the sign alternates, the magnitude may approach zero or another value. Understanding this helps analyze whether the sequence converges or oscillates without settling.
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