English

Arithmetic Series

How to find the value of an arithmetic series (the sum of an arithmetic sequence): formula, 3 examples, and their solutions.

Formula

Examplea = 3, d = 5, n = 20, S20 = ?

Example-1 + 3 + 7 + 10 + ... + 31

ExampleSn = n2 + 2n, an = ?