Question

if a sequence is decreasing, can it still be an arithmetic sequence?
no, unless it is a geometric sequence
yes, if the common difference is positive
yes, if the common difference is negative
no, arithmetic sequences cannot decrease

Explanation:

An arithmetic sequence is defined by a constant common difference $d$ between consecutive terms. If $d < 0$, each term is smaller than the previous one, making the sequence decreasing.

Answer:

Yes, if the common difference is negative