Mathematics

Mathematics

Problem

Consider the series ∑n=1∞npnp+1,\sum_{n=1}^{\infty}\frac{n^{p}}{n^{p}+1}, where pp is a real parameter. For which values of pp does the nnth–term test indicate that the series diverges? a) p≥0p\ge 0 b) p>0p>0 only c) All real numbers pp d) p<0p<0 only
Intuitive explanation

The nnth-term test (divergence test) says a series can only converge if its terms shrink to zero. Here, you need to find when npnp+1\frac{n^p}{n^p+1} does not approach zero as n→∞n \to \infty. The key insight is comparing the growth rates of numerator and denominator: when pp is large enough, npn^p dominates the "+1" in the denominator, so the fraction approaches a nonzero limit. Determine the threshold value of pp where this happens.

Intuitive explanation

The nnth-term test (divergence test) says a series can only converge if its terms shrink to zero. Here, you need to find when npnp+1\frac{n^p}{n^p+1} does not approach zero as n→∞n \to \infty. The key insight is comparing the growth rates of numerator and denominator: when pp is large enough, npn^p dominates the "+1" in the denominator, so the fraction approaches a nonzero limit. Determine the threshold value of pp where this happens.

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