A conclusion of exchangeable random variables

In this paper,the similarity and difference of identically distributed random variables and exchangeable random variables sequences in certain relevant conditions are researched.This paper uses reverse martingale approach to solve the approximate behavior problems of finite exchangeable random variables sequences.As the De Finetti′s theorem states that infinite exchangeable random variables sequences is independent and identically distributed with the condition of the tailσ-algebra.So some results about independent identically distributed random variables is similar to exchangeable random variables.