1. 数列{an}满足a1=1,a2=3,a n+2(n+2是a的下标)=3a n+1(n+1是a的下标)-2an(n∈正整数),证明:数列{a n+1-an }是等比数列2.数列{an}满足an=n×2^n,求前n项和记为Sn(错位相减法)