题目

已知数列｛an}满足a1=2,an-an-1=3n,求an

提问时间：2021-04-01

答案

累加法.an=（an-an-1）+（an-1 - an-2）+·······+（a2-a1）+a1=3n+3（n-1）+······+3*2+2=3（2+3+·····+n）+2=(3n^2+3n-2)/2