An arithmetic sequence has a common DIFFERENCE.
This means that the difference between a term and the previous one is always the same. For example: 1, 4, 7, 10, 13,... This is an arithmetic sequence because the difference between consecutive elements is always 3 (4-1=7-4=10-7=13-10=...=3)
A geometric sequence has a common RATIO.
This means that the ratio between a term and the previous one is always the same. For example: 1, 3, 9, 27, 81,... This is a geometric sequence because the ratio between consecutive elements is always 3
(3/1=9/3=27/9=81/27=...=3).
