Given a sequence, we can form the sum of the first n terms of the sequence, for each positive integer n. This sequence of sums is called a series. In this tutorial, we look at summation notation for sums, and we derive formulas for the sum of the first n terms of arithmetic sequences and geometric sequences. * Aimed at students in their final two years of high school. * Studying mathematics is best done by working through examples and exercises. There are many interactive examples and exerci