Answer:
The formula which can be used to find the sum of the first n terms of a geometric sequence is:

Explanation:
Geometric sequence--
A sequence is said to be a geometric sequence if each of the term of a sequence is a constant multiple of the preceding term of the sequence.
This constant multiple is known as a common ratio and is denoted by r.
Also, if the first term of the sequence is:

Then the sequence is given by:

The sum of the first n terms of the sequence is given by:
