Here, we formally define a geometric series, and then use some clever algebraic trickery to derive a formula for any convergent geometric series. If you watched the previous Numberphile video, Dr. Grime pretty much already did that for you. Duration: 13:07

Need some practice recognizing a convergent geometric series and finding its sum? Here are 3 + 1/2 + 1/4 + 1/8 + 1/16 + ... examples to help you out. Duration: 18:24

In Examples 8 and 9, we look at a repeating decimal as an application of a geometric series, and then get a preview of something called a power series, which can be thought of as a function of convergent geometric series. Duration: 12:35