The infinite sequence a1, a2,…, an,… is such that a1 = 2, a2 = -3, a3 = 5, a4 = -1, and an = an-4 for n > 4. What is the sum of the first 97 terms of the sequence?
72
74
75
78
80
登录 或 注册 后可以参加讨论
每四个数的和=3,97是24*4+1，也就是24个3的和加第一个数的和 24*3+2=74
扫描二维码，直接登录
每四个数的和=3,97是24*4+1，也就是24个3的和加第一个数的和 24*3+2=74