How do you determine if a sequence is geometric

(I told you in the definition)  

A geometric sequence is a sequence in which each term of the sequence is obtained by multiplying/dividing by a common value, called the common ratio, to the preceding term. Given a sequence, we can determine whether the sequence is arithmetic, geometric or neither by comparing the terms of the sequence.

If a sequence is geometric, it will repeat itself.

Examples:

1, 2, 3, 4

3, 9, 27, 81

-1, 3, -9, 27

3, 6, 9, 12

An example of a sequence that is not geometrical would be:

2, 7, 3, 18, 26, 472