Arithmetic Sequence

An arithmetic sequence is a sequence in which, beginning with the second term, each term is found by adding the same value to the previous term. Its general term is described by

a n= a 1 + ( n –1) d

The number d is called the common difference. It can be found by taking any term in the sequence and subtracting its preceding term. 

Example 1

Find the common difference in each of the following arithmetic sequences. Then express each sequence in the form a n = a 1 + (n – 1) d and find the twentieth term of the sequence. 

  1. 1, 5, 9, 13, 17, …
  2. … 
  3. 1, 5, 9, 13, 17, …
  4. Therefore, the twentieth term of the sequence is 
  5. a 20 = 1 + (20 – 1)4 = 1 + 76 = 77 
  6. … 
  7. Since
  8. Then
  9. Therefore, the twentieth term of the sequence is
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