Geometric Series (Jump to: Lecture | Video )

Figure 1.

Imagine you have a secret. You tell 3 friends, who each tell 3 friends, who then tell another 3 friends. This is an example of a geometric series.

Geometric Series: 1 + 3 + 9 + 27, r = 3

Sum of a Geometric Series
The sum of the first n terms of a geometric series is found using the equation: where r cannot be equal to 1.

Let's calculate the sum of the first 9 terms of our geometric series:

Figure 2.