Convergent Series

Definition

A convergent series is a mathematical sequence where the sum of the terms approaches a finite value as the number of terms increases. This concept is crucial in the study of geometric sequences and series, as it determines whether a series will have a defined, finite sum or continue to grow indefinitely.

5 Must Know Facts For Your Next Test

1. A geometric series is convergent if the common ratio $r$ is less than 1, and divergent if the common ratio is greater than or equal to 1.
2. The sum of a convergent geometric series is given by the formula $S = \frac{a}{1-r}$, where $a$ is the first term and $r$ is the common ratio.
3. The partial sums of a convergent series will approach a finite value as the number of terms increases, while the partial sums of a divergent series will continue to grow without bound.
4. Convergence of a series is an important concept in calculus, as it allows for the evaluation of integrals and the study of infinite series.
5. The concept of convergence is also crucial in the study of power series, which are used to approximate functions and solve differential equations.

Review Questions

• Explain the relationship between the common ratio and the convergence of a geometric series.
  • The common ratio $r$ of a geometric series is the key determinant of whether the series will converge or diverge. If the common ratio is less than 1 ($|r| < 1$), the series will converge to a finite sum. However, if the common ratio is greater than or equal to 1 ($|r| \geq 1$), the series will diverge and the sum will grow without bound. This is because a common ratio less than 1 means each term in the series is getting smaller, allowing the series to approach a finite value, while a common ratio greater than or equal to 1 means the terms are either staying the same size or getting larger, causing the series to continue growing indefinitely.
• Describe how the partial sums of a convergent series behave as the number of terms increases.
  • The partial sums of a convergent series, which represent the sum of the first $n$ terms, will approach a finite value as the number of terms $n$ increases. This means that as more terms are added to the series, the partial sum will get closer and closer to the true sum of the infinite series. In contrast, the partial sums of a divergent series will continue to grow without bound as more terms are added, never converging to a finite value. This difference in behavior between convergent and divergent series is a key characteristic that allows us to determine whether a series will have a defined, finite sum or continue to grow indefinitely.
• Explain the importance of convergence in the context of geometric sequences and series, and how it relates to other areas of mathematics.
  • The concept of convergence is fundamental to the study of geometric sequences and series, as it determines whether a series will have a finite, well-defined sum or continue to grow without bound. This is crucial in applications such as calculating the sum of infinite geometric series, which has important uses in calculus, physics, and other areas of mathematics. Additionally, the idea of convergence is essential in the study of power series, which are used to approximate functions and solve differential equations. More broadly, the concept of convergence is a central theme in mathematical analysis, as it underpins the study of limits, integrals, and the behavior of infinite processes. Understanding convergence is therefore a key skill for success in intermediate algebra and beyond.

Related terms

Geometric Series: A geometric series is a series where each term is a constant multiple of the previous term, forming a geometric sequence.

Partial Sum: The partial sum of a series is the sum of the first $n$ terms of the series, which can be used to determine if the series converges or diverges.

Common Ratio: The common ratio of a geometric sequence is the constant ratio between consecutive terms, which is used to determine the convergence or divergence of a geometric series.