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# On line calculation tool of geometric sequence

Category:

an Sn

### APP description

A geometric sequence means that if a sequence is from item 2, the ratio of each item to its previous item is equal to the same constant. This constant is called the ratio of the geometric series，the common ratio is usually represented by the letter q as (q≠0), and the ratio $$a1≠ 0$$. Note: When q=1, an is a constant column.

Geometric sequence formula

1.General formula：$$an=a1q^{n-1}$$

2.Summation formula:

$$Sn=na1$$(q=1)

$$Sn= \frac {a1(1-q^n)}{1-q}$$(q≠1）

### Usage example

The first item of a sequence: 6

Common proportions: 5

Input: 2

Choice: Sn

Click "Calculate" to output the result

The sum of the first 2 is 36.