I didn't want to answer at first, but later I found it interesting, so I started to do it, only to find that I forgot all about it after I was admitted to graduate school for half a year. I can't guarantee it's right, because I'm too lazy to calculate it carefully, but my thinking is definitely right. Please understand. This question is not difficult, but for those of you who have never studied limit and sequence, it really feels difficult. In fact, the high school routine series questions are covered with a series of coats, which are still at the end. Finally, if you don't know how to ask, if I can't see it in time, add me q 103952 1082?