Consider the infinite series

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

Problem

Consider the infinite series S=∑n=1∞1n2+3n\displaystyle S=\sum_{n=1}^{\infty}\frac{1}{n^{2}+3n}. A student computes successive partial sums and records S4=0.6300S_{4}=0.6300 and S5=0.6715S_{5}=0.6715 (rounded to four decimal places). Answer the following questions related to numerical approximation of SS. (a) Describe, in words, what the value of a partial sum SNS_{N} represents in relation to the exact value SS of the series. (b) Given the values of S4S_{4} and S5S_{5} above, explain what inequalities you can state about SS. Justify your answer without calculating additional terms. (c) Write a clear plan (no numerical execution required) for deciding how many terms of the series must be added so that the approximation differs from SS by less than 0.00050.0005.

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