Learning Materials
Explanations
Features
Discover
A sequence is a set of numbers that all follow a rule. You need to know about two different types of sequences arithmetic and geometric sequences.
Achieve better grades quicker with Premium
Geld-zurück-Garantie, wenn du durch die Prüfung fällst
Review generated flashcards
to start learning or create your own AI flashcards
Start learning or create your own AI flashcards
Team Sequences Teachers
Jump to a key chapter
An arithmetic sequence is a sequence that has a common difference, and this means that the sequence will either increase or decrease by a constant addition or subtraction. They look like this:
3, 7, 11, 15, 19 ... This sequence has a common difference of 4
78, 72, 66, 60, 54 ... This sequence has a common difference of 6
5, 12, 19, 26, 33 ... This sequence has a common difference of 7
You may need to find a specific term (nth term) within the sequence and to do this you can use this formula;
\[u_n = a + (n-1)d\]
un is the nth term a is the first term d is the common difference
Find the 50th term of the following sequence 4, 7, 10, 13, 16, 19 ...
First, you need to identify your variables and substitute them into the formula;
n - 50
a - 4
d - 3
\[u_{50} = 4 + (50-1)3\]
Now you need to solve the equation.
\[u_{50} = 4 + (50-1)3\]
\[u_{50} = 151\]
A geometric sequence is a sequence that has a common ratio, the sequence will either increase or decrease by a constant multiplication or division. Here are some examples:
You may also be asked to find a specific term from this sequence, below is the formula that you would need;
\[u_n = ar^{n-1}\]
un is the nth term a is the first term r is the common ratio
Find the 15th term of this sequence 1, 2, 4, 8, 16 ...
First you need to identify your variables and substitute them into the formula;
n - 15
a - 1
r - 2
\[u_{15} = (1)2^{15-1}\]
Now you solve your equation.
\[u_{15} = (1)2^{15-1}\]
\[u_{15} = 16384\]
You are able to find each term of the sequence if you know the rule that it is following and the first term using a recurrence relation. You can use each previous term to help you find the next one, and the formula for this is;
\[u_{n+1} = f(u_n)\]
You may be given this function and asked to find the first number of terms. Let's have a look at how you would approach this type of question;
Find the next five terms of the sequence \(u_{n+1} = u_n + 3, u_1 = 7\)
To do this, you need to substitute the nth term into the formula;
term 1 - \(u_2 = u_1 +3\) \(u_2 = 7 + 3\) \(u_2 = 10\)
term 2 - \(u_3 = u_2 +3\) \(u_3 = 10 + 3\) \(u_3 = 13\)
term 3 - \(u_4 = u_3 +3\) \(u_4 = 13 + 3\) \(u_4 = 16\)
term 4 - \(u_5 = u_4 +3\) \(u_5 = 16 + 3\) \(u_5 = 19\)
term 5 - \(u_6 = u_5 +3\) \(u_6 = 19 + 3\) \(u_6 = 122\)
Sequences can be described as increasing if each term is higher than the previous one, this can be shown as, \(u_{n+1} > u_n\). They can be described as decreasing if each term is less than the previous one, this can be shown as \(u_{n+1} < u_n\). A sequence can also be described as periodic if the terms within the sequence repeat, or create a cycle, this can be shown as \(u_{n+k} = u_n\).
An example of an increasing sequence 7, 15, 23, 31, 39, 47
An example of a decreasing sequence 15, 10, 5, 0, -5, -10
An example of a periodic sequence 8, 9, 10, 8, 9, 10, 8, 9, 10
Sequences can be used to model many real-life scenarios, such as savings and salaries. If the model increases by the same amount, it will create an arithmetic sequence; if it increases by the same percentage, it will create a geometric sequence.
A woman has £2000 in her savings account, and each month, she adds £200. How much money would she have in her savings account after one year?
Let's break down the question. First, we need to identify the type of sequence that it is. As the constant increases by the same amount each month, it is an arithmetic sequence. Next, we need to find the correct formula to use to help us find how much money is in the account after 1 year, meaning you need to find the 12th term;
\[u_n = a + (n-1)d\]
Next you need to substitute in the information that you know
a - 2000
n - 12
d - 200
\[u_{12} = 2000 + (12-1)200\]
Now solve the equation that you have created.
\[u_{12} = 2000 + (12-1)200\]
\[u_{12} = 4200\]
You now know that the woman will have £4200 in her savings account after 12 months.
A sequence is a set of numbers that follow a specific rule and order.
There are two types of sequences, arithmetic and geometric.
An arithmetic sequence increases and decreases by addition and subtraction.
A geometric sequence increases and decreases by multiplication and division.
You can use a formula to find a specific term within the sequence.
Sequences can be used to model real life scenarios.
Sign up for free to gain access to all our flashcards.
What is a sequence?
A sequence is a set of numbers that follow an order and a specific rule.
What is a geometric sequence?
A geometric sequence is a set of numbers that increase or decrease by multiplication or division.
What is the difference between a set and a sequence?
The main difference between the two is that in a sequence the order of the numbers is important, also the numbers can be repeated, whereas a number will only appear once in a set.
At StudySmarter, we have created a learning platform that serves millions of students. Meet the people who work hard to deliver fact based content as well as making sure it is verified.
Digital Content Specialist
Lily Hulatt is a Digital Content Specialist with over three years of experience in content strategy and curriculum design. She gained her PhD in English Literature from Durham University in 2022, taught in Durham University’s English Studies Department, and has contributed to a number of publications. Lily specialises in English Literature, English Language, History, and Philosophy.
Get to know Lily
AI Engineer
Gabriel Freitas is an AI Engineer with a solid experience in software development, machine learning algorithms, and generative AI, including large language models’ (LLMs) applications. Graduated in Electrical Engineering at the University of São Paulo, he is currently pursuing an MSc in Computer Engineering at the University of Campinas, specializing in machine learning topics. Gabriel has a strong background in software engineering and has worked on projects involving computer vision, embedded AI, and LLM applications.
Get to know Gabriel
Flashcards 
StudySmarter AI 
Notes 
Study Plans 
Study Sets 
Exams 
Magazine 
Find a job 
Mobile App