# 4: Infinite Sequences and Series

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IN THIS CHAPTER we consider infinite sequences and series of constants and functions of a real variable.

• SECTION 4.1 introduces infinite sequences of real numbers. The concept of a limit of a sequence is defined, as is the concept of divergence of a sequence to $$\pm\infty$$. We discuss bounded sequences and monotonic sequences. The limit inferior and limit superior of a sequence are defined. We prove the Cauchy convergence criterion for sequences of real numbers.
• SECTION 4.2 defines a subsequence of an infinite sequence. We show that if a sequence converges to a limit or diverges to $$\pm\infty$$, then so do all subsequences of the sequence. Limit points and boundedness of a set of real numbers are discussed in terms of sequences of members of the set. Continuity and boundedness of a function are discussed in terms of the values of the function at sequences of points in its domain.
• SECTION 4.3 introduces concepts of convergence and divergence to $$\pm\infty$$ for infinite series of constants. We prove Cauchy’s convergence criterion for a series of constants. In connection with series of positive terms, we consider the comparison test, the integral test, the ratio test, and Raabe’s test. For general series, we consider absolute and conditional convergence, Dirichlet’s test, rearrangement of terms, and multiplication of one infinite series by another.
• SECTION 4.4 deals with pointwise and uniform convergence of sequences and series of functions. Cauchy’s uniform convergence criteria for sequences and series are proved, as is Dirichlet’s test for uniform convergence of a series. We give sufficient conditions for the limit of a sequence of functions or the sum of an infinite series of functions to be continuous, integrable, or differentiable.
• SECTION 4.5 considers power series. It is shown that a power series that converges on an open interval defines an infinitely differentiable function on that interval. We define the Taylor series of an infinitely differentiable function, and give sufficient conditions for the Taylor series to converge to the function on some interval. Arithmetic operations with power series are discussed.

This page titled 4: Infinite Sequences and Series is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by William F. Trench via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.