In this sequence there are actually two sequences. 1 sequence for the numerators and one sequence for the denominators. The following transformation applies to the sequence for the denominators : +2
This creates the following sequence: [7, 9, 11, 13, 15, 17]
The following transformation applies to the sequence for the numerators: -9
This creates the following sequence: [8, -1, -10, -19, -28, -37]
Take a good look at how to rewrite the fractions in the series to recognize the pattern.
For example, -9/1 can be rewritten as 9/-1