There are various formulas related to various sequences and series by using them we can find a set of unknown values like the first term, nth term, common parameters, etc. These formulas are different for each kind of sequence and series. Formulas related to various sequences and series are explained below:
Arithmetic Sequence and Series Formula
The various formulas used in arithmetic sequence are given below:
| Arithmetic sequence | a, a + d, a + 2d, a + 3d, … |
|---|---|
| Arithmetic series | a + (a + d) + (a + 2d) + (a + 3d) + … |
| First term: | a |
| Common difference(d): | Successive term – Preceding term or an – an-1 |
| nth term, an | a + (n-1)d |
| Sum of arithmetic series, Sn | (n/2)(2a + (n-1)d) |
Geometric Sequence and Series Formulas
The various formulas used in geometric sequence are given below:
| Geometric sequence | a, ar, ar2,….,ar(n-1),… |
|---|---|
| Geometric series | a + ar + ar2 + …+ ar(n-1)+ … |
| First term | a |
| Common ratio | r |
| nth term | ar(n-1) |
| Sum of geometric series | Finite series: Sn = a(1−rn)/(1−r) for r≠1, and Sn = an for r = 1Infinite series: Sn = a/(1−r) for |r| < 1, and not defined for |r| > 1 |