郑爽生日2017张翰:一道极限题目

来源:百度文库 编辑:高考问答 时间:2024/05/09 05:53:17
求2,3,6,11,18,27的通项公式

3 - 2 = 1
6 - 3 = 3
11 - 6 = 5
18 - 11 = 7
27 - 18 = 9

a(n) = a(n-1) + (2n - 3) .........n>1

a(n) = 2 + [(1 + 3 + 5 + .... + (2n - 3)]
= 2 + (n - 2)^2

4n-1