If there is a negative number in an (usually the topic is negative number), we will look at it separately.

Because there are negative numbers in an, Sn is the sum of positive and negative numbers, and the value is definitely smaller than |an|.

But don't worry. |an| in the general topic is very simple, although it should be viewed separately from the positive and negative aspects. You can solve this problem by establishing two new series. As long as you write it on paper, don't just rely on your own brain. It's actually quite simple.