Determine whether the sequence is geometric. If so, find the common ratio.
1. 3, 6, 12, 24, . . .
2. 5, 10, 15, 20, . . .
3. 1 / 27, 1 / 9, 1 / 3, 1, . . .
4. 27, - 9, 3, -1, . . .
5. 1, 1 / 2, 1 / 3, 1 / 4, . . .
6. 5, 1, 0.2, 0.04, . . .
7. 1, - √7, 7, -7 √7, . . .
8. 2, 4 / √3, 8 / 3, 16 / 3 √3, . . .