Question

Which formula can be used to sum the first n terms of a geometric sequence?

Answer 1

Answer:

The correct answer option is B. $S _ n = a _ 1 [ \frac { 1 - r ^ n } { 1 - r } ]$.

Step-by-step explanation:

The following is the formula that is used to find the sum of a geometric progession:

$S _ n = a _ 1 [ \frac { 1 - r ^ n } { 1 - r } ]$

where $S_n$ is the sum, $a_1$ is the first term, $r$ is the common ratio while $n$ is the number of terms.

Answer 2

Answer:

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

          $S_n=a_1(\dfrac{1-r^n}{1-r})$

Step-by-step 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: $a_1$

Then the sequence is given by:

$a_1,\ a_2=a_1r,\ a_3=a_1r^2,\ a_4=a_1r^3,\ .............a_n=a_1r^{n-1},\ .....$

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

$S_n=a_1(\dfrac{1-r^n}{1-r})$