85.8k views
5 votes
what is the recursive formula for a geometric sequence is an=2a n-1 with an initial value of an=2a n-1 with an initial value of a1=1/8 what is the explicit formula for the sequence?

1 Answer

5 votes

Answer: To find the explicit formula for the geometric sequence with the recursive formula an = 2an-1 and a1 = 1/8, we can use the following steps:

First, we can write out the first few terms of the sequence using the recursive formula:

a1 = 1/8

a2 = 2a1 = 2/8 = 1/4

a3 = 2a2 = 2/4 = 1/2

a4 = 2a3 = 2/2 = 1

a5 = 2a4 = 2

We can see that the common ratio between any two consecutive terms is 2, so we can write:

a2/a1 = 2

a3/a2 = 2

a4/a3 = 2

a5/a4 = 2

In general, we can write the ratio of any two consecutive terms as:

an/an-1 = 2

We can use this to find an expression for an in terms of a1:

a2/a1 = 2

a2 = 2a1

a3/a2 = 2

a3 = 2a2 = 2(2a1) = 4a1

a4/a3 = 2

a4 = 2a3 = 2(4a1) = 8a1

a5/a4 = 2

a5 = 2a4 = 2(8a1) = 16a1

In general, we can write:

an = 2^(n-1) * a1

Substituting a1 = 1/8, we get:

an = 2^(n-1) * (1/8) = 1/(2^(8-n))

Therefore, the explicit formula for the geometric sequence is:

an = 1/(2^(8-n))

Explanation:

User Mate Varga
by
7.0k points

No related questions found

Welcome to QAmmunity.org, where you can ask questions and receive answers from other members of our community.

9.4m questions

12.2m answers

Categories