Given:
-9, -2, 5, 12, …
The difference between -9 and -2 is
[tex]-2-(-9)=-2+9=7[/tex]
The difference between -2 and 5 is
[tex]5-(-2)=5+2=7[/tex]
The difference between 5 and 12 is
[tex]12-5=7[/tex]
The difference between each term is the same value 7.
Hence we get the common difference d =7.
The given sequence is an arithmetic sequence since it has a common difference.
