I need to know whether or not 15, 13, 11, 9, ... is an arithmetic sequence

Answer: Yes

Step-by-step explanation: An arithmetic sequence is a sequence that has a common difference. The common difference is the number that is repeatedly added or subtracted to reach the next term in the sequence.

In this sequence, notice that we start with 15. Then, we subtract 2 to reach our next term which is 13. Next, we subtract 2 to get to our next term which is 11. In the same way, we subtract 2 from 11 to reach our next term, 9.

The dot dot dots just mean that this sequence goes on forever so to answer your question, this is indeed an arithmetic sequence.