Answer:
C
Step-by-step explanation:
For a sequence to be arithmetic it must have a common difference d between consecutive terms.
Sequence 1
- 3, 1, 5, 9, ....
d = 1 - (- 3) = 1 + 3 = 4
d = 5 - 1 = 4
d = 9 - 5 = 4
d = 4 hence arithmetic sequence
Sequence 2
1, 2, 4, 8, ....
2 - 1 = 1
4 - 2 = 2
8 - 4 = 4
There is no common difference, thus not arithmetic but in fact geometric.
Sequence 3
4, - 12, 36, - 108, ....
- 12 - 4 = - 16
36 - (- 12) = 36 + 12 = 48
- 108 - 36 = - 144
There is no common difference, hence not arithmetic, but geometric
Sequence 4
7, 14, 21, 28
d = 14 - 7 = 7
d = 21 - 14 = 7
d = 28 - 21 = 7
d = 7 hence arithmetic sequence
1 and 4 are arithmetic sequences → C
