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Math Lesson 12.4.2 - Converging and Diverging Infinite Series

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Welcome to our Math lesson on Converging and Diverging Infinite Series, this is the second lesson of our suite of math lessons covering the topic of Infinite Series Explained, you can find links to the other lessons within this tutorial and access additional Math learning resources below this lesson.

Converging and Diverging Infinite Series Explained

Some number series have a finite value despite having an infinite number of terms. They are called converging infinite series. For example, geometric series with a fractional common ratio smaller than 1 are infinite series, as the terms become smaller and smaller; the increase in sum becomes more and more irrelevant. A typical infinite series is

S = 1/2 + 1/4 + 1/8 + 1/16 + 1/64 + 1/128 + 1/256 + 1/512 + 1/1024 + ⋯

This series points towards the value 1, as first we take half of the whole, then half of the remaining half and so on, as illustrated in the figure below.

Math Tutorials: Infinite Series Explained Example

This is because the divisions remain always within the original square, regardless of the number of partitions made. Hence, we can write

S = 1/2 + 1/4 + 1/8 + 1/16 + 1/64 + 1/128 + 1/256 + 1/512 + 1/1024 + ⋯ = 1

The condition for an infinite series to be convergent is that

n = 1xn = L

where L is a finite number. (In the previous example L = 1.)

Example 1

What is the value of

1/4 + 1/8 + 1/16 + 1/32 + ⋯

Solution 1

From the example, in theory, we can write

1/4 + 1/8 + 1/16 + 1/32 + ⋯
= (1/2 + 1/4 + 1/8 + 1/16 + 1/32 + ⋯)-1/2
= 1 - 1/2
= 2/2 - 1/2
= 1/2

More Infinite Series Explained Lessons and Learning Resources

Sequences and Series Learning Material
Tutorial IDMath Tutorial TitleTutorialVideo
Tutorial
Revision
Notes
Revision
Questions
12.4Infinite Series Explained
Lesson IDMath Lesson TitleLessonVideo
Lesson
12.4.1Infinite and Finite Number Series
12.4.2Converging and Diverging Infinite Series
12.4.3Calculating an Infinite Geometric Series
12.4.4The Comparison Test of Convergence
12.4.5The Special Types of Infinite Series
12.4.6The Ratio Convergence Test
12.4.7The Root Convergence Test

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