Arithmetic Sequences And Series

A series of free, online lessons for Intermediate Algebra (Algebra II) with videos, examples and solutions.

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Related Pages
Number Sequences
Linear Sequences
Quadratic and Cubic Sequences
More Lessons for Algebra II

In these lessons, we will learn

  • about arithmetic sequences
  • how to find the formula for the nth term of an arithmetic sequence
  • about arithmetic series
  • how to find the sum of an arithmetic series

The following diagram gives the Arithmetic Sequence Formula. Scroll down the page for more examples and solutions on how to use the Arithmetic Sequence Formula to find the nth term of the sequence.

Arithmetic Sequence

What Is An Arithmetic Sequence?

A list of numbers that follows a rule is called a sequence. Sequences whose rule is the addition of a constant are called arithmetic sequences, similar to geometric sequences that follow a rule of multiplication.

Homework problems on arithmetic sequences often ask us to find the nth term of a sequence using a formula. Arithmetic sequences are important to understanding arithmetic series.

Arithmetic Sequences

Determine the nth term of an arithmetic sequence.
Determine the common difference of an arithmetic sequence.
Determine the formula for an arithmetic sequence.
An arithmetic sequence is a sequence that has the pattern of adding a constant to determine consecutive terms. We say arithmetic sequences have a common difference.


  1. A sequence is a function. What is the domain and range of the following sequence?
  2. Given the formula for the arithmetic sequence, determine the first 3 terms and the 8th term. Also state the common difference.
    an = -4n + 3
  3. Given the arithmetic sequence, determine the formula and the 12th term
    -2,1.5,5,8.5,12,15.5, …

Introduction To Arithmetic Sequences

Just a quick idea of what an arithmetic sequence is and a few examples.

Determine which of the following sequences are arithmetic. If they are arithmetic, give the value of ’d'.

  1. 3,8,13,18,23,28,33, …
  2. -.7, -1.7, -2.7, -3.7, -4.7, …
  3. 1.6, 2.2, 2.8, 3.3, 3.9, 4.5, …
  4. 4/3, 5/3, 2, 7/3, 8/3, 3, …

Arithmetic Sequences: A Formula For The ‘nth’ Term

This video derives the formula to find the ‘n-th’ term of a sequence by considering an example.
The formula is then used to do a few different problems.

Suppose we have the arithmetic sequence
3, 8, 13, 18, 23, 28, 33, …

How To Find The General Term Of An Arithmetic Sequence?

an = a1 + (n-1)d

What Is An Arithmetic Series?

We can use what we know of arithmetic sequences to understand arithmetic series. An arithmetic series is a series or summation that sums the terms of an arithmetic sequence.

There are methods and formulas we can use to find the value of an arithmetic series.

Understanding arithmetic series can help to understand geometric series, and both concepts will be used when learning more complex Calculus topics.

Arithmetic Series

Define a series.
Determine the partial sum of an arithmetic series.
Summing or adding the terms of an arithmetic sequence creates what is called a series.
Sn = n/2(an + an)

Determine the sum of the arithmetic series

  1. 3 + 8 + 13 + … + 73
  2. an = -4n + 3; n = 20

How To Find The Sum Of An Arithmetic Series?

How to find the sum of an arithmetic series when you’re given only the first few terms and the last one?

Find the sum
-82, -80, -78, … +64, +66

Try the free Mathway calculator and problem solver below to practice various math topics. Try the given examples, or type in your own problem and check your answer with the step-by-step explanations.
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