Series

The series of a sequence is the sum of the sequence to a certain number of terms. It is often written as Sn.  So if the sequence is 2, 4, 6, 8, 10, ... , the sum to 3 terms = S3 = 2 + 4 + 6 = 12.

The Sigma Notation

The Greek capital sigma, written S, is usually used to represent the sum of a sequence. This is best explained using an example:

This means replace the r in the expression by 1 and write down what you get. Then replace r by 2 and write down what you get. Keep doing this until you get to 4, since this is the number above the S. Now add up all of the term that you have writ ...