What is the recursive formula for this arithmetic sequence

Recursion is the process of choosing a starting term and repeatedly applying the same process to each term to arrive at the following term. Recursion requires that you know the value of the term immediately before the term you are trying to find.

Speaking about the Arithmetic Sequence Recursive Formula, it has two parts: first, a starting value that begins the sequence and a recursion equation that shows how terms of the sequence related to the preceding terms.

The recursive formula for an arithmetic sequence with common difference d is;

Arithmetic Sequence Recursive formula may list the first two or more terms as starting values depending upon the nature of the sequence. However, the an portion is also dependent upon the previous two or more terms in the sequence.

Examples Using the Formula for Arithmetic Sequence Recursive

Here are a few example questions:

Example 1:

Write the first four terms of the sequence when: a1= – 4 and an = an−1 + 5

Solution:

In recursive formulas, each term is used to produce the next term. Follow the movement of the terms through the steps given below.

Given:

a1= – 4

And

an = an−1 + 5 (each term is 5 more than the term before)

n = 2

a2= a2−1 + 5

a2 = -4 +5

a2 = 1

n = 3

a3 = a3−1 + 5

a3 = 1 + 5

a3 = 6

n = 4

a4 = a4−1 + 5

a4 = 6 + 5

a4 = 11

Answer: -4, 1, 6, 11

Example 2: Find the recursive formula when the sequence 2, 4, 6, 8, 10….

Solution:

Considering this sequence, it can be represented in more than one manner. The given sequence can be represented as either an explicit (general) formula or a recursive formula.

Explicit Formula: an = 2n

Recursive Formula: a1 = 2 and an = an−1 + 2

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So I have learned to program using recursion, but I have not learned how to actually do this in math. If I have the sequence {4,8,12}, and the question asks for a recursive formula to solve for an+1, would it be as simple as: an+1 = an + 4 ? This seems correct to me, but it also seems too simple.

asked Nov 16, 2016 at 23:36

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If the explicit formula for a sequence is $a_n=a_1+n(d-1)$, then the recursive formula is $a_n=a_{n-1}+d$. Here, we have that the explicit formula is $a_n=4+4(n-1)$, then the recursive formula will be $a_n=a_{n-1}+4$. You are correct.

answered Mar 25, 2020 at 18:58

4yl1n4yl1n

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We saw in Sequences - Basic Information, that sequences can be expressed in various forms.
This page will look at one of those forms, the recursive form.

Certain sequences (not all) can be defined (expressed) in a "recursive" form.
In a recursive formula, each term is defined as a function of its preceding term(s).
[Each term is found by doing something to the term(s) immediately in front of that term.]

A recursive formula designates the starting term, a1, and the nth term of the sequence, an , as an expression containing the previous term (the term before it), an-1.


The process of recursion can be thought of as climbing a ladder.
To get to the third rung, you must step on the second rung. Each rung on the ladder depends upon stepping on the rung below it.
You start on the first rung of the ladder. a1
From the first rung, you move to the second rung. a2
    a2
= a1 + "step up"
From the second rung, you move to the third rung. a3
    a3 = a2 + "step up"

What is the recursive formula for this arithmetic sequence

If you are on the nth rung, you must have stepped on the n-1st rung.    an = an-1 + "step up"

What is the recursive formula for this arithmetic sequence

Notation: Recursive forms work with the term(s) immediately in front of the term being examined. The table at the right shows that there are many options as to how this relationship may be expressed in notations.

A recursive formula is written with two parts: a statement of the first term along with a statement of the formula relating successive terms.

The statements below are all naming the same sequence:

What is the recursive formula for this arithmetic sequence

Given Term

Term in front
of Given Term

a4

a3

an

an-1

an+1

an

an+4

an+3

f (6)

f (5)

f (n)

f (n-1)

f (n+1)

f (n)

What is the recursive formula for this arithmetic sequence
Sequence: {10, 15, 20, 25, 30, 35, ...}. Find a recursive formula.
This example is an arithmetic sequence(the same number, 5, is added to each term to get to the next term).

Term Number

Term

Subscript Notation

Function Notation

1

10

a1

f (1)

2

15

a2

f (2)

3

20

a3

f (3)

4

25

a4

f (4)

5

30

a5

f (5)

6

35

a6

f (6)

n

What is the recursive formula for this arithmetic sequence

an

f (n)

Recursive Formulas:
in subscript notation: a1 = 10; an = an-1+ 5
in function notation: f (1) = 10; f (n)= f (n-1)+ 5

What is the recursive formula for this arithmetic sequence


Arithmetic sequences are
linear in nature. Remember that the domain consists of the natural numbers, {1, 2, 3, ...}, and the range consists of the terms of the sequence. It may be the case with arithmetic sequences that the graph will increase or decrease.

 
What is the recursive formula for this arithmetic sequence

In most arithmetic sequences, a recursive formula is easier to create than an explicit formula. The common difference is usually easily seen, which is then used to quickly create the recursive formula.

What is the recursive formula for this arithmetic sequence
What is the recursive formula for this arithmetic sequence

To summarize the process of writing a recursive formula for an arithmetic sequence:
1. Determine if the sequence is arithmetic (Do you add, or subtract, the same amount from one term to the next?)
2.
Find the common difference. (The number you add or subtract.)
3. Create a recursive formula by stating the first term, and then stating the formula to be the previous term plus the common difference.

a1 = first term;
an= an-1 + d

a1 = the first term in the sequence
an = the nth term in the sequence
an-1 = the term before the nth term
n = the term number
d = the common difference.

What is the recursive formula for this arithmetic sequence

{10, 15, 20, 25, 30, 35, ...}

first term = 10, common difference = 5
recursive formula: a1= 10; an= an-1 + 5

What is the recursive formula for this arithmetic sequence

What is the recursive formula for this arithmetic sequence
Sequence: {3, 6, 12, 24, 48, 96, ...}. Find a recursive formula.
This example is a geometric sequence (the same number, 2, is multiplied times each term to get to the next term).

Term Number

Term

Subscript Notation

Function Notation

1

3

a1

f (1)

2

6

a2

f (2)

3

12

a3

f (3)

4

24

a4

f (4)

5

48

a5

f (5)

6

96

a6

f (6)

n

What is the recursive formula for this arithmetic sequence

an

f (n)

Recursive Formulas:
in subscript notation: a1 = 3; an = 2 • an-1
in function notation: f (1) = 3; f (n) = 2 • f (n-1)

What is the recursive formula for this arithmetic sequence


Notice that this sequence has an
exponential appearance.
It may be the case with geometric sequences that the graph will increase or decrease.


To summarize the process of writing a recursive formula for a geometric sequence:
1. Determine if the sequence is geometric (Do you multiply, or divide, the same amount from one term to the next?)
2.
Find the common ratio. (The number you multiply or divide.)
3. Create a recursive formula by stating the first term, and then stating the formula to be the common ratio times the previous term.

a1 = first term;
an= r • an-1

a1 = the first term in the sequence
an = the nth term in the sequence
an-1 = the term before the nth term
n = the term number
r = the common ratio

What is the recursive formula for this arithmetic sequence

{3, 6, 12, 24, 48, 96, ...}

first term = 3, common ratio = 2
explicit formula: an= 3 • 2n-1

What is the recursive formula for this arithmetic sequence

What is the recursive formula for this arithmetic sequence
Sequence: {0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, ...}
This example is neither an arithmetic sequence nor a geometric sequence.

What is the recursive formula for this arithmetic sequence

While we have seen recursive formulas for arithmetic sequences and geometric sequences, there are also recursive forms for sequences that do not fall into either of these categories.

The sequence shown in this example is a famous sequence called the Fibonacci sequence.

Is there a pattern for the Fibonacci sequence?
Yes. After the first two terms, each term is the sum of the previous two terms.

Is there a recursive formula for the Fibonacci sequence?
Yes.  f (1) = 0;   f (2) = 1;   f (n)= f (n - 1) + f (n - 2)  
 or      
        a1
= 0;     a2 = 1;    an = an-1 + an-2

What is the recursive formula for this arithmetic sequence

Notice that it was necessary to declare the first and second term, before stating the formula for generating the remaining terms.

What is the recursive formula for this arithmetic sequence

Arrow down to
"In Func MODE"


What is the recursive formula for this arithmetic sequence


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How do you write a recursive formula for an arithmetic sequence?

A recursive sequence is a sequence in which terms are defined using one or more previous terms which are given. If you know the nth term of an arithmetic sequence and you know the common difference , d , you can find the (n+1)th term using the recursive formula an+1=an+d .

What is a recursive formula?

a formula for determining the next term of a sequence from one or more of the preceding terms.

What is a recursive rule for a sequence?

A recursive rule for a sequence is a formula which tells us how to progress from one term to the next in a sequence. Generally, the variable is used to represent the term number. In other words, takes on the values 1 (first term), 2 (second term), 3 (third term), etc.