Arithmetic Sequences 

A sequence in which term after the first is formed by adding a fixed number to the preceding term is called arithmetic sequence. The fixed number or constant is called the common difference denoted by 𝒅. 

To find the common difference (d), you can simply subtract 

• the second term (𝑎2 ) by the first term (𝑎1 ), 𝑎2 - 𝑎1, or 

• the third term (𝑎3 )by the second term (𝑎2 ), 𝑎3 - 𝑎2 , or 

• the fourth term (𝑎4 )by the third term (𝑎3 ), 𝑎4- 𝑎3, or 

• in general, a term (𝑎𝑛) by its preceding term (𝑎𝑛−1) 𝑑 = 𝑎𝑛 − 𝑎𝑛−1.