Tell whether each sequence is an arithmetic sequence or not? If it is arithmetic sequence, find the common difference.
1. 3, 7, 11, 15, 19
2. 4, 16, 64, 256
3. 48, 24, 12, 6, 3, ...
4. 2, 4, 8, 16, ...
5. 9.5, 7.5, 5.5, 3.5, ...
6. 1, 0, -1, -2, -3
7. 4, 10, 16, 22, ...
8. 11, 2, -7, -16, ... 1/2
9. 1,1,0,1,... 2
10. x/3 x/9 3x, x...​