A geometric progression is a sequence in which each term is derived by multiplying or dividing the preceding term by a fixed number called the common ratio. E.g., the height to which a ball rises in each successive bounce follows a geometric progression. The sequence 4, -2, 1,... is a Geometric Progression (GP) for which (-1/2) is the common ratio. We can use the concept to find an arbitrary term, a finite or infinite sum of the series, and apply them in various contexts, including some difficult problems.

- The general form of a GP is a, ar, ar
^{2}, ar^{3}and so on. Thus nth term of a GP series is T_{n}= ar^{n-1}, where a = first term and r = common ratio = T_{m}/T_{m-1}.

If the common ratio is:
###### Geometric Progression Formula

- Negative: the result will alternate between positive and negative.
- Greater than 1: there will be an exponential growth towards infinity (positive).
- Less than -1: there will be an exponential growth towards infinity (positive and negative).
- Between 1 and -1: there will be an exponential decay towards zero.
- Zero: the result will remain at zero

Must Read Geometric Progressions Articles

- Geometric Progressions: Concept & Tricks
- Geometric Progressions: Solved Examples

Suppose that we want to find the sum of the first n terms of a geometric progression. What we get is

sum of GP: Sn = a + ar + ar^{2} + ar^{3} + . . . + ar^{n-1 }

- The GP series formula applied to calculate the sum of geometric progression of first
*n*terms of a GP:

and

Suggested Action:

- When three quantities are in GP, the middle one is called as the geometric mean of the other two. If a, b and c are three quantities in GP and b is the geometric mean of a and c i.e.

- The sum of infinite GP series: