Consider the infinite series S(p)= _ n=1 ^ 1 n^ p (p R )

MATHEMATICS · Multi-part · AP · Calculus BC · Infinite Sequences and Series · Infinite Sequences and Series

Problem

Consider the infinite series S(p)=∑n=1∞1np(p∈R).S(p)=\sum_{n=1}^{\infty}\frac{1}{n^{p}}\quad (p\in\mathbb{R}). This classic one–parameter family provides a benchmark for comparing more complicated series. (a) Determine all real numbers pp for which the sequence of terms an=1npa_n=\dfrac{1}{n^{p}} approaches 00 as n→∞n\to\infty. Justify your answer. (b) For which values of pp does the series S(p)S(p) converge? For which values does it diverge? Provide a complete explanation that references the behavior of an appropriate improper integral without actually evaluating that integral explicitly. (c) Describe, in clear prose, how the critical value of pp you found in part (b) serves as a threshold separating two qualitatively different long–run behaviors for S(p)S(p).

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