Question

How to tell if a sequence is arithmetic or geometric

Answer 1

If the series is arithmetic the second term minus the first term must equal the third term minus the second term.
If the series is Geometric the second term divided by the first term must equal the third term divided by the second term.

Answer 2

For a given sequence
`a_n` find the value of
`a_(n+1)`.

Then:
If
`a_(n+1)-a_n=\text{const}` then the sequence is arithmetic.
If
`(a_(n+1))/(a_n)=\text{const}` then the sequence is geometric.