# How to write a recursive rule for geometric sequence

In this lesson, it is assumed that you know what an arithmetic sequence is and can find a common difference. Find a6, a9, and a12 for problem 4.

I like how Purple Math so eloquently puts it: Notice that the an and n terms did not take on numeric values. In this situation, we have the first term, but do not know the common ratio. This video is all about two very special Recursive Sequences: Find the recursive formula for 5, 10, 20, 40.

Rather than write a recursive formula, we can write an explicit formula. Look at the example below to see what happens. Find the explicit formula for 0. The first term in the sequence is 2 and the common ratio is 3.

Whereas, in a Geometric Sequence each term is obtained by multiply a constant to the preceding term. An Arithmetic Sequence is such that each term is obtained by adding a constant to the preceding term.

Now we use the formula to get Notice that writing an explicit formula always requires knowing the first term and the common ratio. Notice this example required making use of the general formula twice to get what we need.

In the beginning we will learn how to write terms for an Arithmetic or Geometric Sequence when we are given either the common difference or the common ratio. This sounds like a lot of work. However, we have enough information to find it.

The first time we used the formula, we were working backwards from an answer and the second time we were working forward to come up with the explicit formula.

When writing the general expression for a geometric sequence, you will not actually find a value for this. Then, we either subtract or divide these two adjacent terms and viola we have our common difference or common ratio.

This constant is called the Common Difference. The formula says that we need to know the first term and the common ratio. Using the recursive formula, we would have to know the first 49 terms in order to find the 50th. Order of operations tells us that exponents are done before multiplication.

What is your answer?Recursive sequences can be hard to figure out, so generally they'll give you fairly simple ones of the "add a growing amount to get the next term" or "add the last two or three terms together" type: Find the next number in the sequence: 3, 2, 5, 7, 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 in the sequence to determine other terms.

So once you know the common ratio in a geometric 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.

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.

A recursive sequence is a sequence in which terms are defined using one or more previous terms which are given. (n + 1) th term using the recursive formula a n + 1 = a n + d.

Write the first four terms of the geometric sequence whose first term is a 1 = 3 and whose common ratio is r = 2. Find the recursive formula of an arithmetic sequence given the first few terms.

Practice: Recursive formulas for arithmetic sequences. Introduction to geometric sequences Site Navigation.

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How to write a recursive rule for geometric sequence
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