This topic examines the basic knowledge and skills of arithmetic progression and geometric progression's general formula and its first N terms and formulas. This paper mainly examines the reasoning ability, computing ability and "sum of split terms", which also needs to be discussed in categories. This is a difficult question, but it is very simple for you to think carefully and think carefully in a crisis. The answer is/exercise/math /804284. I didn't quite understand this question at first, and I often forgot some key points.

It is known that the tolerance of arithmetic progression {an is 2, the sum of the first n terms is Sn, S 1, s 2 and S3 are geometric series.

(1) Find the general term formula of sequence {an

(2) let bn = (-1) (n-1) 4n/Anan+1,and find the first n terms of the sequence {bn} and t n.

I still hope everyone can accept my suggestion, thank you.