Label each of the following as arithmetic, geometric, or neither and tell why.

{a_n} = 1, -2, 3, -4, 5, -6, 7, …

{b_n} = 1, -2, 4, -8, 16, …

{c_n}= 1, 2, 3, 4, 5, …

{d_n}= 27, 18, 12, 8, 16/3, …

{e_n}= 1, -1, 1, -1, 1, -1, …

{f_n} = 10, 8, 6, 4, …

1. neither
2. geometric
3. arithmetic
4. geometric
5. geometric
6. arithmetic