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Here we will learn about how to find the nth term of a sequence. Youβll learn what the nth term is and how to work it out from number sequences and patterns.
At the end youβll find nth term worksheets based on Edexcel, AQA and OCR exam questions, along with further guidance on where to go next if youβre still stuck.
The nth term is a formula that enables us to find any term in a sequence. It refers to the position of a term in a sequence. For example, the first term has n=1, the second term has n=2, the 10th term has n=10 and so on. The ‘n’ stands for its number in the sequence.
We can make a sequence using the nth term by substituting different values for the term number(
To find the 20th term we would follow the sequence formula but substitute 20 instead of ‘
For example if the
1st term
2nd term
3rd term
10th term = 2(10) + 1 = 21
Below are a few examples of different types of sequences and their
Type of Sequence | Example | nth Term |
---|---|---|
Arithmetic | 6, 2, -2, -6, -10, ... | 10-4n |
Geometric | 1, 2, 4, 8, 16, 32, ... | 2^{n-1} |
Quadratic | 3, 9, 19, 33, 51, ... | 2n^{2}+1 |
Cubic | 2, 22, 78, 188, 370, ... | 3n^{3}-n |
In this lesson, we will look specifically at finding the
Get your free nth term worksheet of 20+ questions and answers. Includes reasoning and applied questions.
DOWNLOAD FREEGet your free nth term worksheet of 20+ questions and answers. Includes reasoning and applied questions.
DOWNLOAD FREENth term of a sequence is part of our series of lessons to support revision on sequences. You may find it helpful to start with the main sequences lesson for a summary of what to expect, or use the step by step guides below for further detail on individual topics. Other lessons in this series include:
To find the nth term of a sequence, use the formulaΒ an=a1+(nβ1)d.
Here’s how to understand using this nth term formula to find the nth term.
The nth term of an arithmetic sequence is given by:
a_{n}=a_{1}+(n-1) dTo find the nth term, first calculate the common difference,
Next multiply each term number of the sequence
Then add or subtract a number from the new sequence to achieve a copy of the sequence given in the question.
This will give you the
To summarise, in order to find the
Where,
a_{n} is the n^{th} term (general term)
a_{n} is the first term
n is the term position
d is the common difference
Where,
a_{n} is the n^{th} term (general term)
a_{1} is the first term
n is the term position
r is the common ratio
Where,
a, b and c are constants (numbers on their own)
n is the term position
a + b + c is the first term
3a + b is the first difference between
2a is the second difference
Find the
Here,
The common difference
2 Multiply the values for
Here, we generate the sequence
3 Add or subtract a number to obtain the sequence given in the question.
The
Find the
Find the common difference for the sequence.
Here,
The common difference
Multiply the values for n = 1, 2, 3, … by the common difference.
Here, we generate the sequence
Β Add or subtract a number to obtain the sequence given in the question.
The
Find the
Find the common difference for the sequence.
Here,
The common difference
Multiply the values for n = 1, 2, 3, … by the common difference.
Here, we generate the sequence
Β Add or subtract a number to obtain the sequence given in the question.
The
Find the
Find the common difference for the sequence.
Here,
The common difference
Multiply the values for n = 1, 2, 3, … by the common difference.
Here, we generate the sequence
Β Add or subtract a number to obtain the sequence given in the question.
The
Find the
Find the common difference for the sequence.
Here
The common difference
Multiply the values for n = 1, 2, 3, … by the common difference.
Here, we generate the sequence
Β Add or subtract a number to obtain the sequence given in the question.
The
Using the patterns below, write an expression for the number of lines in pattern
Find the common difference for the sequence.
By counting the number of sides we can see that the first term in the sequence is
The second term in the sequence is
The next term
Here,
The common difference
Multiply the values for n = 1, 2, 3, … by the common difference.
Here, we generate the sequence
Β Add or subtract a number to obtain the sequence given in the question.
The
For example, the sequence
For example, if the
For example, taking the decreasing sequence
1. Write down the first three terms in the sequence 4n – 7 .
2. Below is a table describing the position of each term in an arithmetic sequence and the value of these terms.
State the value of the first term in the sequence.
\begin{aligned} &\quad n \quad \quad 1 \quad \quad2 \quad \quad 3 \quad \quad 4 \quad \quad 5 \\ &an + b \quad \quadΒ \quad 8.7 \quad 15.9 \quad \quad \quad 30.3 \end{aligned}
It is an arithmetic sequence meaning the difference between each term is the same.
15.9-8.7 = 7.2 so the difference between each term is 7.2 .
8.7-7.2=1.5 therefore the first term is 1.5 .
3. Below are the first 5 terms of an arithmetic sequence.
8, \quad 13, \quad 18, \quad 23, \quad 28, …Find the n^{th} Β term of the sequence.
The common difference here is 5 so it is 5n .
To get from 5n to our sequence we need to add 3 so our sequence is 5n+3 .
4. Find the n^{th} term formula of the sequence:
-10, \quad-20, \quad -30 \quad -40 \quad -50, …
The common differenceΒ is -10 so it is -10n .Β
We do not need to add or subtract anything here so the nth term is just -10n .
5. The number of petals on a sunflower can be represented as a linear sequence.
Write an expression for the number of petals on sunflower n .
The number of petals on the first three flowers are 5, 7 and 9 .
We need to find the n^{th} term of this sequence.
The common difference is 2 so it is 2n .
We need to add 3 to the sequence 2n so the expression is 2n+3 .
6. The number of square tiles around a pool generates an arithmetic sequence.
How many tiles would there be around a pool of width 30 ?
Around the first three pools, the number of tiles are 8, 12 and 16 .
The n^{th} Β formula for this sequence is 4n+4.
Substituting n = 30 , 4 \times 30 + 4 = 124 .
7. Find the n^{th} term of the linear sequence:
2 \frac{1}{3}, \; \; 2 \frac{2}{3}, \; \; 3, \; \; 3 \frac{1}{3}, \; \; 3 \frac{2}{3}, \ldots
The common difference is \frac{1}{3} so it isΒ \frac{1}{3} n .
Another way of writing this is \frac{n}{3} .
1.Β A sequence of patterns is made using triangles.
(a) What is the n^{th} term formula for the number of triangles?
(b) How many dark purple triangles would there be in pattern number 100 ?
(3 marks)
(a)
Sequence 1, 3, 5, 7 – common difference is 2
(1)
2n – 1
(1)
(b)
99 (one less than the pattern number)
(1)
2.Β (a)Β Write down an expression for the n^{th} Β term of the following sequence:
-4, -1, 2, 5, 8, β¦.
(b)Β Is the number 101 in this sequence? Show how you decide.
(4 marks)
(a)
Common difference is 3
(1)
3n-7
(1)
(b)
3nΒ βΒ 7 = 101
(1)
\begin{aligned} 3n&=108\\\\ n&=36 \end{aligned}
Yes it is the 36th term
(1)
3. The n^{th} Β of a sequence is 2n + 3 .
The n^{th} Β of a different sequence is 5n β 2 .
There are two numbers under 30 that appear in both sequences. What are the two numbers?
(3 marks)
2n + 3: 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29,.. Β
(1)
5n β 2: 3, 8, 13, 18, 23, 28, …
(1)
13 Β and 23
(1)
You have now learned how to:
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