The constant q is called the common ratio. In geometric series, the first term a 1 and the common ratio q are not zero. The sum formula of equal proportion series is the formula for finding the sum of geometric progression.

If a series starts from the second term, the ratio of each term to its previous term is equal to the same constant. This series is called geometric series, and this constant is called the common ratio of geometric series. Formula can quickly calculate the sum of this series.

A series, if the ratio of any last item to the previous item is the same constant (this constant is usually expressed by Q) and any item in the series cannot be 0.