Question

趣味题-找规律0,1/2,-6,12,0.05,-30,42,1/56,-72,······第50个数应为几?不光要答案

Answer 1

2,5,8,...项的分数先倒数来看,

3,6,9项的负数变为正数看规律：

0,2,6,12,20,30,42,56,72

后项减前项：2,4,6,8,10,12,14,16.

所以此为(n-1)n,因此规律为：

A(3n+1)=3n(3n+1)

A(3n+2)=1/[(3n+1)(3n+2)]

A(3n+3)=-(3n+2)(3n+3)

n=0,1,2,3,.