9/17 15/34 6/17 9/34 geometric sequence?

In a geometric sequence each number after the first is found by multiplying the previous number by a fixed number called the common ratio.

In an arithmetic sequence, each term is equal to the previous term plus or minus a constant called the common difference.

In your problem we have a sequence of numbers that appears to be decreasing in value, but on the surface it doesn't appear to be by any constant number... but if you look closely, the denominator 34 is exactly twice the other denominator 17. This would lead me to look at a common denominator to see if anything takes shape...

9/17 = 18/34
15/34
6/17 = 12/34
9/34

Now we see that each number is the previous number minus 3/34, so we have a common difference of 3/34.

This would match the definition of an arithmetic sequence and NOT a geometric sequence.

Two because two of one thing is two.