Since an arithmetic sequence is a sequence of numbers and the difference of any two successive members of the sequence is a constant
So this question is arithmetic because it keep minus by 7
from 19 - 7 = 12
12 - 7 = 5
5 - 7 = -2
so common difference is -7
or you can check with arithmetic formular as
=
+ (n−1)d
I will just put in the 4th term which is -2 and n will equal to 4
and is the 1st term which is 19
-2 = 19 + (4−1)d
-2 - 19 = 3d
d =
d = -7