What Is The Rule For Arithmetic Sequence? (TOP 5 Tips)

an+1= an + d, d — . : , d.

Contents

What is the rule of arithmetic sequence?

An arithmetic sequence is a sequence where the difference between each successive pair of terms is the same. The explicit rule to write the formula for any arithmetic sequence is this: an = a1 + d (n – 1)

How do you find a rule for a sequence?

To work out the term to term rule, give the starting number of the sequence and then describe the pattern of the numbers. The first number is 3. The term to term rule is ‘ add 4’. Once the first term and term to term rule are known, all the terms in the sequence can be found.

What is the rule for the nth term of the arithmetic sequence?

The nth term of an arithmetic sequence is given by. an = a + (n – 1)d. The number d is called the common difference because any two consecutive terms of an. arithmetic sequence differ by d, and it is found by subtracting any pair of terms an and. an+1.

What is the sum formula for arithmetic sequence?

An arithmetic sequence is defined as a series of numbers, in which each term (number) is obtained by adding a fixed number to its preceding term. Sum of arithmetic terms = n/2[2a + (n – 1)d], where ‘a’ is the first term, ‘d’ is the common difference between two numbers, and ‘n’ is the number of terms.

How do you solve arithmetic mean?

One method is to calculate the arithmetic mean. To do this, add up all the values and divide the sum by the number of values. For example, if there are a set of “n” numbers, add the numbers together for example: a + b + c + d and so on. Then divide the sum by “n”.

Arithmetic Sequences and Sums

A sequence is a collection of items (typically numbers) that are arranged in a specific order. Each number in the sequence is referred to as aterm (or “element” or “member” in certain cases); for additional information, see Sequences and Series.

Arithmetic Sequence

An Arithmetic Sequence is characterized by the fact that the difference between one term and the next is a constant. In other words, we just increase the value by the same amount each time. endlessly.

Example:

1, 4, 7, 10, 13, 16, 19, 22, and 25 are the numbers 1 through 25. Each number in this series has a three-digit gap between them. Each time the pattern is repeated, the last number is increased by three, as seen below: As a general rule, we could write an arithmetic series along the lines of

  • There are two words: Ais the first term, and dis is the difference between the two terms (sometimes known as the “common difference”).

Example: (continued)

1, 4, 7, 10, 13, 16, 19, 22, and 25 are the numbers 1 through 25. Has:

  • In this equation, A = 1 represents the first term, while d = 3 represents the “common difference” between terms.

And this is what we get:

Rule

It is possible to define an Arithmetic Sequence as a rule:x n= a + d(n1) (We use “n1” since it is not used in the first term of the sequence).

Example: Write a rule, and calculate the 9th term, for this Arithmetic Sequence:

3, 8, 13, 18, 23, 28, 33, and 38 are the numbers three, eight, thirteen, and eighteen. Each number in this sequence has a five-point gap between them. The values ofaanddare as follows:

  • A = 3 (the first term)
  • D = 5 (the “common difference”)
  • A = 3 (the first term).

Making use of the Arithmetic Sequencerule, we can see that_xn= a + d(n1)= 3 + 5(n1)= 3 + 3 + 5n 5 = 5n 2 xn= a + d(n1) = 3 + 3 + 3 + 5n n= 3 + 3 + 3 As a result, the ninth term is:x 9= 5 9 2= 43 Is that what you’re saying? Take a look for yourself! Arithmetic Sequences (also known as Arithmetic Progressions (A.P.’s)) are a type of arithmetic progression.

Advanced Topic: Summing an Arithmetic Series

To summarize the terms of this arithmetic sequence:a + (a+d) + (a+2d) + (a+3d) + (a+4d) + (a+5d) + (a+6d) + (a+7d) + (a+8d) + (a+9d) + (a+9d) + (a+9d) + (a+9d) + (a+9d) + (a+9d) + ( make use of the following formula: What exactly is that amusing symbol? It is referred to as The Sigma Notation is a type of notation that is used to represent a sigma function. Additionally, the starting and finishing values are displayed below and above it: “Sum upnwherengoes from 1 to 4,” the text states. 10 is the correct answer.

Example: Add up the first 10 terms of the arithmetic sequence:

The values ofa,dandnare as follows:

  • In this equation, A = 1 represents the first term, d = 3 represents the “common difference” between terms, and n = 10 represents the number of terms to add up.

As a result, the equation becomes:= 5(2+93) = 5(29) = 145 Check it out yourself: why don’t you sum up all of the phrases and see whether it comes out to 145?

Footnote: Why Does the Formula Work?

Let’s take a look at why the formula works because we’ll be employing an unusual “technique” that’s worth understanding. First, we’ll refer to the entire total as “S”: S = a + (a + d) +. + (a + (n2)d) +(a + (n1)d) + (a + (n2)d) + (a + (n1)d) + (a + (n2)d) + (a + (n1)d) + (a + (n1)d) + (a + (n2)d) + (a + (n1)d) + (a + (n1)d) + (a + (n1)d) + After that, rewrite S in the opposite order: S = (a + (n1)d)+ (a + (n2)d)+. +(a + d)+a. +(a + d)+a. +(a + d)+a. Now, term by phrase, add these two together:

S = a + (a+d) + . + (a + (n-2)d) + (a + (n-1)d)
S = (a + (n-1)d) + (a + (n-2)d) + . + (a + d) + a
2S = (2a + (n-1)d) + (2a + (n-1)d) + . + (2a + (n-1)d) + (2a + (n-1)d)

Each and every term is the same!

Furthermore, there are “n” of them. 2S = n (2a + (n1)d) = n (2a + (n1)d) Now, we can simply divide by two to obtain the following result: The function S = (n/2) (2a + (n1)d) is defined as This is the formula we’ve come up with:

Algebra II Recipe: Arithmetic Sequences

  1. Sequences are a list of numbers in a specific order
  2. Terms are the numbers in the sequence. If a variable is preceded by a subscript number, the term’s position in the sequence is indicated, for example, 7 denotes the 7th term. The n th term is indicated by a nand is the general term denoted by a n the series in which the difference “d” between consecutive terms is constant
  3. The sequence in which the difference “d” between consecutive words is constant
  • Arithmetic sequences are formed when there is a common difference of 5 between the numbers 4, 9, 14, 19, 24, and so on. Arithmetic sequences are formed when there is a common difference of -3 between the numbers 17, 14, 11, 8, 5, and so on.
  1. An equation that allows you to locate any term in a series is known as a rule.

In the case of an Arithmetic Sequence, the following rule applies: a 1+ (n – 1)d

  1. A n is the n thterm in the series
  2. A 1 is the first term of the sequence
  3. N is the number of terms in the sequence
  4. D is the common difference
  5. And n is the number of terms in the sequence To write the rule, just the a 1 and d values should be used.
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C. Creating a Rule When You Only Have the Arithmetic Sequence As Information

  1. Calculate the values of a 1 and d
  2. Substitute the values of a 1 and d into the equation a n= a 1+ (n – 1)d
  3. Reduce the complexity of the equation
D. Writing a Rule When You Know Some Term In the Arithmetic Sequence and the Common Difference.
  1. 1 is obtained by putting the provided information into a n= an n+1 + (n – 1)d. Only the a 1 and d values should be substituted into a n= a 1+ (n – 1)d
  2. Reduce the complexity of the equation
E. Writing a Rule When You Only Know Two Terms in the Arithmetic Sequence.
  • N= a 1+ (n – 1)d is substituted into Eq. 1 for the biggest n, and n= a 1+ (n – 1)d is substituted into Eq. 2 for the smallest n, and so on.
  1. Simplify each equation
  2. Subtract the equations (Eq. 1-Eq. 2) to arrive at d
  3. Simplify each equation again. In order to determine a 1, substitute the value of d intoEq. 2 (the “smallest equation”). Substitute the values of a 1 and d into the equation a n= a 1+ (n – 1)d
  4. Simplify the expression

Arithmetic Sequence Formula – What is Arithmetic Sequence Formula? Examples

Calculating the nth term of an arithmetic progression is accomplished through the use of the arithmetic sequence formula. The arithmetic sequence is a series in which the common difference between any two succeeding terms remains constant throughout the sequence. In order to discover any term in the arithmetic sequence, we may use the arithmetic sequence formula, which is defined as follows: Let’s look at several solved cases to better grasp the arithmetic sequence formula.

What Is the Arithmetic Sequence Formula?

An Arithmetic sequence has the following structure: a, a+d, a+2d, a+3d, and so on up to n terms. In this equation, the first term is called a, the common difference is called d, and n = the number of terms is written as n. Recognize the arithmetic sequence formulae and determine the AP, first term, number of terms, and common difference before proceeding with the computation. Various formulae linked with an arithmetic series are used to compute the n thterm, total, or common difference of a given arithmetic sequence, depending on the series in question.

Arithmetic Sequence Formula

The arithmetic sequence formula is denoted by the notation Formula 1 is a racing series that takes place on the track. The arithmetic sequence formula is written as (a_ =a_ +(n-1) d), where an is the number of elements in the series.

  • In the following formula, we have the arithmetic sequence formula. Formula 1 is a racing series in which drivers compete against one other. This is the formula for the arithmetic sequence: (a_ =a_ +(n-1) d), where a_ is the number of elements in the series.

The n thterm formula of anarithmetic sequence is sometimes known as the n thterm formula of anarithmetic sequence. For the sum of the first n terms in an arithmetic series, the formula is (S_ = frac), where S is the number of terms.

  • (S_ ) is the sum of n terms
  • (S_ ) is the sum of n terms
  • A is the initial term, and d is the difference between the following words that is common to all of them.

Formula 3: The formula for determining the common difference of an AP is given as (d=a_ -a_ )where, a_ is the AP’s initial value and a_ is the common difference of the AP.

  • There are three terms in this equation: nth term, second last term, and common difference between the consecutive terms, denoted by the letter d.

Formula 4: When the first and last terms of an arithmetic progression are known, the sum of the first n terms of the progression is given as, (s_ = fracleft )where, and

  • In arithmetic progressions, if the first and last terms are known, the sum of the first n terms of an arithmetic progression is given by the formula (s_ = fracleft)where,

Applications of Arithmetic Sequence Formula

Each and every day, and sometimes even every minute, we employ the arithmetic sequence formula without even recognizing it. The following are some examples of real-world uses of the arithmetic sequence formula.

  • Arranging the cups, seats, bowls, or a house of cards in a towering fashion
  • There are seats in a stadium or a theatre that are set up in Arithmetic order
  • The seconds hand on the clock moves in Arithmetic Sequence, as do the minutes hand and the hour hand
  • The minutes hand and the hour hand also move in Arithmetic Sequence. The weeks in a month follow the AP, and the years follow the AP as well. It is possible to calculate the number of leap years simply adding 4 to the preceding leap year. Every year, the number of candles blown on a birthday grows in accordance with the mathematical sequence

Consider the following instances that have been solved to have a better understanding of the arithmetic sequence formula. Do you want to obtain complicated math solutions in a matter of seconds? To get answers to difficult queries, you may use our free online calculator. Find solutions in a few quick and straightforward steps using Cuemath. Schedule a No-Obligation Trial Class.

Examples Using Arithmetic Sequence Formula

In the first example, using the arithmetic sequence formula, identify the thirteenth term in the series 1, 5, 9, and 13. Solution: To locate the thirteenth phrase in the provided sequence. Due to the fact that the difference between consecutive terms is the same, the above sequence is an arithmetic series. a = 1, d = 4, etc. Making use of the arithmetic sequence formula (a_ =a_ +(n-1) d) = (a_ =a_ +(n-1) d) = (a_ =a_ +(n-1) d) For the thirteenth term, n = 13(a_ ) = 1 + (13 – 1) 4(a_ ) = 1 + 4(a_ ) (12) The sum of 4(a_ ) and 48(a_ ) equals 49.

Example 2: Determine the first term in the arithmetic sequence in which the 35th term is 687 and the common difference between the two terms.

Solution: In order to locate: The first term in the arithmetic sequence is called the initial term.

Example 3: Calculate the total of the first 25 terms in the following sequence: 3, 7, 11, and so on.

In this case, (a_ ) = 3, d = 4, n = 25. The arithmetic sequence that has been provided is 3, 7, 11,. With the help of the Sum of Arithmetic Sequence Formula (S_ =frac), we can calculate the sum of the first 25 terms (S_ =frac) as follows: (25/2) = 25/2 102= 1275.

FAQs on Arithmetic Sequence Formula

It is referred to as arithmetic sequence formula when it is used to compute the general term of an arithmetic sequence as well as the sum of all n terms inside an arithmetic sequence.

What Is n in Arithmetic Sequence Formula?

It is important to note that in the arithmetic sequence formula used to obtain the generalterm (a_ =a_ +(n-1) d), n refers to how many terms are in the provided arithmetic sequence.

What Is the Arithmetic Sequence Formula for the Sum of n Terms?

The sum of the first n terms in an arithmetic series is denoted by the expression (S_ =frac), where (S_ ) =Sum of n terms, (a_ ) = first term, and (d) = difference between the first and second terms.

How To Use the Arithmetic Sequence Formula?

Determine whether or not the sequence is an AP, and then perform the simple procedures outlined below, which vary based on the values known or provided:

  • On determine whether or not the sequence is an AP, do the simple procedures outlined below, which vary according to the values known or provided:

Intro to arithmetic sequences

What I want to accomplish in this video is introduce us to a very typical class of sequences that we will encounter in the future. This is an example of arithmetic sequences. Furthermore, they are typically rather straightforward to identify. They are sequences in which each term is a defined number of times greater than the term before it, as seen in the diagram. So my aim is to figure out which of these sequences are arithmetic sequences in order to do this. In order to give us some practice with the sequence notation, I’d want to define them either as explicit functions of the phrase you’re looking for, the index you’re looking at, or as recursive definitions, just so we can get some practice with it as well.

  • Let’s have a look at this first one, which is located over here.
  • Then, in order to move from negative 3 to negative 1, you must multiply by 2.
  • As a result, it is evident that this is an arithmetic series.
  • And there are a number of other ways in which we may define the sequence.
  • Furthermore, you are not need to utilize the letter k.
  • From n = 1 to infinity with—and there are two ways to define it—we have a problem.
  • We might thus write a sub n equals whatever the first word is to describe it explicitly if we wanted to be specific about what we meant.

In this case, it’s equal to negative 5 plus—we’ll add 2 one less time than the term we’re now at.

For the third term, we multiply by 2 times more.

As a result, we’re planning to add 2.

It follows that the following is an explicit definition of this arithmetic series Alternatively, if I wanted to state it in a recursive manner, I might say that a sub 1 equals negative 5.

Each phrase is equivalent to the preceding term—not 3-plus-2, but 3-plus-3.

In other words, each of these options is a perfectly legal approach to define the arithmetic sequence that we have here.

Take a look at the following sequence.

We’re starting from the beginning.

107 to 114, we’re going to add 7.

As a result, this is a valid arithmetic sequence.

For example, if we want to define it specifically, we could write that this is the sequence a sub n, n running from 1 to infinity of- and we could simply say that a sub n is equal to 100 plus we’re adding 7 every time, if we don’t want to express it properly.

In the third term, we multiply by 7 times.

It is so explicitly defined here, but we could instead define it recursively in the following way: Simply said, this is one definition where we express it like this, or we could write a subn, which would be from n = 1 to infinity, or something similar.

I could also claim that a sub 1 is equal to 100 if I wanted to define it in a recursive manner.

And with that, we’re done.

Assuming you’re looking for a generalizable approach to identify or describe an arithmetic sequence, you might state that an arithmetic sequence is going to have the form a sub n- if we’re talking about an infinite series- from n equals 1 to infinity.

It would be some constant plus some number that you are incrementing- alternatively, I assume, this might be a negative number or decrementing by- times n minus 1.

As a result, this is one method of defining an arithmetic sequence.

In this situation, the value of d is 7.

And in this situation, k is a negative 5, and in this case, k is a hundred (k).

In the case of n larger than or equal to 2, the provided term is equal to the preceding term plus d.

This is the recursive approach of putting things into words.

Now, the remaining question I have is whether or not this series over here is an arithmetic sequence.

We’ll start with the number one.

Then we add three more.

Now we’re going to add a fourth.

So, first and foremost, this is not arithmetic in any way.

But, given that we’re attempting to define our sequences, how would we go about doing so?

Consequently, we may argue that this is equivalent to a sub n, where n begins at 1 and continues to infinity, with—call let’s it our base case—a sub 1 equal to 1.

As a result, a sub 2 equals the previous term plus 2, a sub 3 equals the previous phrase plus 3, and a sub 4 equals the previous term plus 4.

Consequently, while this appears to be a close match, keep in mind that the quantity that we’re adding varies depending on our index.

Thus, when n is higher than or equal to 2, this is the case.

In the case of an arithmetic series, we’re always adding the same amount, regardless of where we are in the sequence. We’re going to add the index itself here. As a result, this is not an arithmetic sequence, but it is an intriguing one anyway.

Formulas for Arithmetic Sequences

  • Create a formal formula for an arithmetic series using explicit notation
  • Create a recursive formula for the arithmetic series using the following steps:

Using Explicit Formulas for Arithmetic Sequences

Formalize an arithmetic sequence into an explicit formula; Create a recursive formula for the arithmetic sequence using the information you’ve received.

A General Note: Explicit Formula for an Arithmetic Sequence

For the textterm of an arithmetic sequence, the formula = +dleft can be used to express it explicitly.

How To: Given the first several terms for an arithmetic sequence, write an explicit formula.

  1. Find the common difference between the two sentences, – To solve for = +dleft(n – 1right), substitute the common difference and the first term into the equation

Example: Writing then th Term Explicit Formula for an Arithmetic Sequence

Create an explicit formula for the arithmetic sequence.left 12text 22text 32text 42text ldots right 12text 22text 32text 42text ldots

Try It

For the arithmetic series that follows, provide an explicit formula for it. left With the use of a recursive formula, several arithmetic sequences may be defined in terms of the preceding term. The formula contains an algebraic procedure that may be used to determine the terms of the series. We can discover the next term in an arithmetic sequence by utilizing a function of the term that came before it using a recursive formula. In each term, the previous term is multiplied by the common difference, and so on.

The initial term in every recursive formula must be specified, just as it is with any other formula.

A General Note: Recursive Formula for an Arithmetic Sequence

In the case of an arithmetic sequence with common differenced, the recursive formula is as follows: the beginning of the sentence = +dnge 2 the finish of the sentence

How To: Given an arithmetic sequence, write its recursive formula.

  1. To discover the common difference between two terms, subtract any phrase from the succeeding term. In the recursive formula for arithmetic sequences, start with the initial term and substitute the common difference

Example: Writing a Recursive Formula for an Arithmetic Sequence

Write a recursive formula for the arithmetic series in the following format: left

How To: Do we have to subtract the first term from the second term to find the common difference?

No. We can take any phrase in the sequence and remove it from the term after it. Generally speaking, though, it is more customary to subtract the first from the second term since it is frequently the quickest and most straightforward technique of determining the common difference.

Try It

Create a recursive formula for the arithmetic sequence using the information provided. left

Find the Number of Terms in an Arithmetic Sequence

When determining the number of terms in a finite arithmetic sequence, explicit formulas can be employed to make the determination. Finding the common difference and determining the number of times the common difference must be added to the first term in order to produce the last term of the sequence are both necessary steps.

How To: Given the first three terms and the last term of a finite arithmetic sequence, find the total number of terms.

  1. Find the common differences between the two
  2. To solve for = +dleft(n – 1right), substitute the common difference and the first term into the equation Fill in the blanks with the final word from and solve forn

Example: Finding the Number of Terms in a Finite Arithmetic Sequence

The number of terms in the infinite arithmetic sequence is to be determined. left

Try It

The number of terms in the finite arithmetic sequence has to be determined. 11 text 16 text. text 56 right 11 text 16 text 16 text 56 text 56 text 56 Following that, we’ll go over some of the concepts that have been introduced so far concerning arithmetic sequences in the video lesson that comes after that.

Solving Application Problems with Arithmetic Sequences

In many application difficulties, it is frequently preferable to begin with the term instead of_ as an introductory phrase. When solving these problems, we make a little modification to the explicit formula to account for the change in beginning terms. The following is the formula that we use: = +dn = = +dn

Example: Solving Application Problems with Arithmetic Sequences

Every week, a kid under the age of five receives a $1 stipend from his or her parents. His parents had promised him a $2 per week rise on a yearly basis.

  1. Create a method for calculating the child’s weekly stipend over the course of a year
  2. What will be the child’s allowance when he reaches the age of sixteen

Try It

A lady chooses to go for a 10-minute run every day this week, with the goal of increasing the length of her daily exercise by 4 minutes each week after that.

Create a formula to predict the timing of her run after n weeks has passed. In eight weeks, how long will her daily run last on average?

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Summary: Arithmetic Sequences

recursive formula for nth term of an arithmetic sequence _ = _ +dphantom}nge 2
explicit formula for nth term of an arithmetic sequence begin_ = _ +dleft(n – 1right)end

Key Concepts

  • An arithmetic sequence is a series in which the difference between any two successive terms is a constant
  • An example would be The common difference is defined as the constant that exists between two successive terms. It is the number added to any one phrase in an arithmetic sequence that creates the succeeding term that is known as the common difference. The terms of an arithmetic series can be discovered by starting with the first term and repeatedly adding the common difference
  • A recursive formula for an arithmetic sequence with common differencedis provided by = +d,nge 2
  • A recursive formula for an arithmetic sequence with common differencedis given by = +d,nge 2
  • As with any recursive formula, the first term in the series must be specified
  • Otherwise, the formula will fail. An explicit formula for an arithmetic sequence with common differenced is provided by = +dleft(n – 1right)
  • An example of this formula is = +dleft(n – 1right)
  • When determining the number of words in a sequence, it is possible to apply an explicit formula. In application situations, we may modify the explicit formula to = +dn, which is a somewhat different formula.

Glossary

When the difference between any two successive words is a constant, this is referred to as a “arithmetic sequence.” The common difference is defined as the constant that exists between two successive terms; It is the number added to each term in an arithmetic sequence that creates the subsequent term that is known as the common difference. Beginning with the first term and adding the common difference repeatedly, the terms of an arithmetic series can be discovered. One way to express the common differenced in an arithmetic series is to use the recursive formula: = +d,nge 2; another way is to use the formula: = +d,nge 2; another way is to use the formula: As with any recursive formula, the first term in the series must be specified; otherwise, the sequence will fail.

It is common for us to slightly modify the explicit formula when solving application difficulties, such as by changing it to = +dn.

Arithmetic Sequences and Series

HomeLessonsArithmetic Sequences and Series Updated July 16th, 2020
Introduction Sequences of numbers that follow a pattern of adding a fixed number from one term to the next are called arithmetic sequences. The following sequences are arithmetic sequences:Sequence A:5, 8, 11, 14, 17,.Sequence B:26, 31, 36, 41, 46,.Sequence C:20, 18, 16, 14, 12,.Forsequence A, if we add 3 to the first number we will get the second number.This works for any pair of consecutive numbers.The second number plus 3 is the third number: 8 + 3 = 11, and so on.Forsequence B, if we add 5 to the first number we will get the second number.This also works for any pair of consecutive numbers.The third number plus 5 is the fourth number: 36 + 5 = 41, which will work throughout the entire sequence.Sequence Cis a little different because we need to add -2 to the first number to get the second number.This too works for any pair of consecutive numbers.The fourth number plus -2 is the fifth number: 14 + (-2) = 12.Because these sequences behave according to this simple rule of addiing a constant number to one term to get to another, they are called arithmetic sequences.So that we can examine these sequences to greater depth, we must know that the fixed numbers that bind each sequence together are called thecommon differences.

Mathematicians use the letterdwhen referring to these difference for this type of sequence.Mathematicians also refer to generic sequences using the letteraalong with subscripts that correspond to the term numbers as follows:This means that if we refer to the fifth term of a certain sequence, we will label it a 5.a 17is the 17th term.This notation is necessary for calculating nth terms, or a n, of sequences.Thed -value can be calculated by subtracting any two consecutive terms in an arithmetic sequence.where n is any positive integer greater than 1.Remember, the letterdis used because this number is called thecommon difference.When we subtract any two adjacent numbers, the right number minus the left number should be the same for any two pairs of numbers in an arithmetic sequence. To determine any number within an arithmetic sequence, there are two formulas that can be utilized.Here is therecursive rule.The recursive rule means to find any number in the sequence, we must add the common difference to the previous number in this list.Let us say we were given this arithmetic sequence.

First, we would identify the common difference.We can see the common difference is 4 no matter which adjacent numbers we choose from the sequence.To find the next number after 19 we have to add 4.19 + 4 = 23.So, 23 is the 6th number in the sequence.23 + 4 = 27; so, 27 is the 7th number in the sequence, and so on.What if we have to find the 724th term?This method would force us to find all the 723 terms that come before it before we could find it.That would take too long.So, there is a better formula.It is called theexplicit rule.So, if we want to find the 724th term, we can use thisexplicit rule.Our n-value is 724 because that is the term number we want to find.The d-value is 4 because it is thecommon difference.Also, the first term, a 1, is 3.The rule gives us a 724= 3 + (724 – 1)(4) = 3 + (723)(4) = 3 + 2892 = 2895. Each arithmetic sequence has its own unique formula.The formula can be used to find any term we with to find, which makes it a valuable formula.To find these formulas, we will use theexplicit rule.Let us also look at the following examples.Example 1 : Let’s examinesequence Aso that we can find a formula to express its nth term.If we match each term with it’s corresponding term number, we get: The fixed number, which is referred to as the common differenceor d-value, is three.

  • We may use this information to replace the explicit rule in the code.
  • a n = a 1 + a (n – 1) the value of da n= 5 + (n-1) (3) the number 5 plus 3n – 3a the number 3n + 2a the number 3n + 2 When asked to identify the 37th term in this series, we would compute for a 37 in the manner shown below.
  • Exemple No.
  • In this case, issequence B.
  • a n= 5n + 21a 14= 5(14) + 21a 14= 70 + 21a 14= 91ideo:Finding the nth Term of an Arithmetic Sequence uizmaster:Finding Formula for General Term It may be necessary to calculate the number of terms in a certain arithmetic sequence.

+ 128.In order to use the sum formula.We need to know a few things.We need to know n, the number of terms in the series.We need to know a 1, the first number, and a n, the last number in the series.We do not know what the n-value is.This is where we must start.To find the n-value, let’s use the formula for the series.We already determined the formula for the sequence in a previous section.We found it to be a n= 3n + 2.We will substitute in the last number of the series and solve for the n-value.a n= 3n + 2128 = 3n + 2126 = 3n42 = nn = 42There are 42 numbers in the series.We also know the d = 3, a 1= 5, and a 42= 128.We can substitute these number into the sum formula, like so.S n= (1/2)n(a 1+ a n)S 42= (1/2)(42)(5 + 128)S 42= (21)(133)S 42= 2793This means the sum of the first 42 terms of the series is equal to 2793.Example 2 : Find the sum of the first 205 multiples of 7.First we have to figure out what our series looks like.We need to write multiples of seven and add them together, like this.7 + 14 + 21 + 28 +.

+?To find the last number in the series, which we need for the sum formula, we have to develop a formula for the series.So, we will use theexplicit ruleor a n= a 1+ (n – 1)d.We can also see that d = 7 and the first number, a 1, is 7.a n= a 1+ (n – 1)da n= 7 + (n – 1)(7)a n= 7 + 7n – 7a n= 7nNow we can find the last term in the series.We can do this because we were told there are 205 numbers in the series.We can find the 205th term by using the formula.a n= 7na n= 7(205)a n= 1435This means the last number in the series is 1435.It means the series looks like this.7 + 14 + 21 + 28 +.

+ 1435To find the sum, we will substitute information into the sum formula.

We will substitute a 1= 7, a 205= 1435, and n = 205.S n= (1/2)n(a 1+ a n)S 42= (1/2)(205)(7 + 1435)S 42= (1/2)(205)(1442)S 42= (1/2)(1442)(205)S 42= (721)(205)S 42= 147805This means the sum of the first 205 multiples of 7 is equal to 147,805.

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