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

Problem

The function ff is defined by f(x)=11−5xf(x)=\dfrac{1}{1-5x}. (a) Rewrite f(x)f(x) as an infinite series of powers of xx that converges for xx near 00. Clearly indicate the first four non-zero terms using sigma notation or expanded form. (b) Provide a justification, based on the structure of your series in part (a), for the radius of convergence of the series. State the corresponding interval of xx-values on which the series representation is valid. (c) Explain, without additional calculation, how the coefficients of xnx^{n} in your series would change if ff were replaced by g(x)=11+5xg(x)=\dfrac{1}{1+5x}. Illustrate your explanation with the first three non-zero terms of the new series.

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