# How to write a recursive formula for a shifted geometric sequence

Shares66 This video is all about two very special Recursive Sequences: Arithmetic and Geometric Sequences. A Recursive equation is a formula that enables us to use known terms in the sequence to determine other terms. Site Navigation Arithmetic Sequences This lesson will work with arithmetic sequences, their recursive and explicit formulas and finding terms in a sequence.

In this lesson, it is assumed that you know what an arithmetic sequence is and can find a common difference. If you need to review these topics, click here.

This arithmetic sequence has a common difference of 4, meaning that we add 4 to a term in order to get the next term in the sequence. The recursive formula for an arithmetic sequence is written in the form For our particular sequence, since the common difference d is 4, we would write So once you know the common difference in an arithmetic sequence you can write the recursive form for that sequence.

However, the recursive formula can become difficult to work with if we want to find the 50th term. Using the recursive formula, we would have to know the first 49 terms in order to find the 50th. This sounds like a lot of work. There must be an easier way. Rather than write a recursive formula, we can write an explicit formula. The explicit formula is also sometimes called the closed form.

To write the explicit or closed form of an arithmetic sequence, we use an is the nth term of the sequence. When writing the general expression for an arithmetic sequence, you will not actually find a value for this.

To find the explicit formula, you will need to be given or use computations to find out the first term and use that value in the formula.

For example, when writing the general explicit formula, n is the variable and does not take on a value. But if you want to find the 12th term, then n does take on a value and it would be You will either be given this value or be given enough information to compute it.

You must substitute a value for d into the formula. You must also simplify your formula as much as possible. Write the explicit formula for the sequence that we were working with earlier.

The first term in the sequence is 20 and the common difference is 4.

## Geometric sequences

This is enough information to write the explicit formula. Now we have to simplify this expression to obtain our final answer. So the explicit or closed formula for the arithmetic sequence is. Notice that an the and n terms did not take on numeric values.

Look at the example below to see what happens. Given the sequence 20, 24, 28, 32, 36. To find the 50th term of any sequence, we would need to have an explicit formula for the sequence. Since we already found that in Example 1, we can use it here. If we do not already have an explicit form, we must find it first before finding any term in a sequence.

This will give us Notice how much easier it is to work with the explicit formula than with the recursive formula to find a particular term in a sequence. What happens if we know a particular term and the common difference, but not the entire sequence? The formula says that we need to know the first term and the common difference.

We have d, but do not know a1. However, we have enough information to find it.The recursive formula for a geometric sequence is written in the form For our particular sequence, since the common ratio (r) is 3, we would write So once you know the common ratio in a geometric sequence you can write the recursive form for that sequence.

Using Recursive Formulas for Geometric Sequences. A recursive formula allows us to find any term of a geometric sequence by using the previous term. Each term is the product of the common ratio and the previous term. For example, suppose the common ratio is 9. Arithmetic and Geometric Sequences 17+ Amazing Examples!. This video is all about two very special Recursive Sequences: Arithmetic and Geometric Sequences. A Recursive equation is a formula that enables us to use known terms . Learn how to find recursive formulas for arithmetic sequences. For example, find the recursive formula of 3, 5, 7, If you're seeing this message, it means we're having trouble loading external resources on our website.

Formula for Shifted Geometric Squence. Ask Question. up vote 1 down vote favorite. How to deduce the recursive derivative formula of B-spline basis?

About this calculator. Definition: Geometric sequence is a list of numbers where each term is obtained by multiplying the previous term by a constant. If a sequence is recursive, we can write recursive equations for the sequence. Recursive equations usually come in pairs: the first equation tells us what the first term is, and the second equation tells us how to get the n th term in . Jun 26,  · A geometric sequence is a sequence derived by multiplying the last term by a constant. Geometric progressions have many uses in today's society, such as calculating interest on money in a bank Geometric progressions have many uses in today's society, such as calculating interest on money in a bank account%(92).

2. Why is Form\$(x)\$ a Primitive recursive relation? 2. Finding the limit of a recursive sequence using a . Jul 10,  · This video screencast was created with Doceri on an iPad. Doceri is free in the iTunes app store. Learn more at srmvision.com

Geometric sequences calculator that shows steps