# How to calculate the sum of a series

In mathematics, a series refers to the sum of the terms in a sequence. In this article, we will explore different methods on how to calculate the sum of a series, including arithmetic and geometric progressions, as well as methods for calculating infinite and converging series.

**1. Arithmetic Series**

An arithmetic series is the sum of consecutive terms in an arithmetic progression, wherein each term’s difference from one to the next is constant. To calculate the sum of an arithmetic series, use the formula:

**S_n = n × (a_1 + a_n) / 2**

where:

– S_n is the sum of the first n terms,

– n is the number of terms,

– a_1 is the first term, and

– a_n is the nth term.

**Example:** Calculate the sum of the first 10 terms in the arithmetic progression 3, 6, 9, …

**S_10 = 10 × (3 + 30) / 2 = 165**

**2. Geometric Series**

A geometric series is the sum of consecutive terms in a geometric progression, where each term’s ratio from one to the next is constant. To calculate the sum of a geometric series, use one of two formulas:

**For r ≠** 1:

**S_n =** a_1 × (1 – r^n) / (1 – r)

**For r =** 1:

**S_n =** n × a_1

**where:**

– S_n is the sum of first n terms,

– n is the number of terms,

– a_1 is the first term,

– r is the common ratio.

**Example:** Calculate the sum of first five terms in geometric progression 2, 4, 8, …

**S_5** = 2 × (1 – (2^5)) / (1 – 2) = 62

**3. Infinite Series**

An infinite series is the sum of an infinite number of terms in a sequence. An infinite series converges if the sum approaches a finite value. To calculate the sum of an infinite geometric series, use the following formula, provided that |r| < 1:

**S_inf = a_1 / (1 – r)**

where:

– S_inf is the sum of the infinite series,

– a_1 is the first term, and

– r is the common ratio.

**Example:** Calculate the sum of an infinite geometric series 1/2, 1/4, 1/8, …

**S_inf =** (1 / 2) / (1 – (1 / 2)) = 1

**4. Convergent Series**

Some specific infinite series converge, such as power series, Taylor series, and alternating series. To calculate these sums, various techniques tailored to each type are employed like integration and differentiation.

In summary, calculating the sum of a series depends on understanding its nature – whether it’s arithmetic or geometric, finite or infinite. Once you identify these characteristics, you can use the appropriate formula to determine the sum with ease. From solving mathematical problems to understanding real-life applications involving accumulated growth and decay processes mastering these techniques can open up a world of opportunities for you to explore in math and beyond!