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 : -10

This creates the following sequence: [7, -3, -13, -23, -33, -43]

The following transformation applies to the sequence for the numerators: +9

This creates the following sequence: [12, 21, 30, 39, 48, 57]

Take a good look at how to rewrite the fractions in the series to recognize the pattern.

For example, -1/7 can be rewritten as -3/21