有关数列的题

题目

有关数列的题
1.Sn=2n^2+3n+1,求An

答案

Sn=2n^2+3n+1
S(n-1)=2(n-1)^2+3(n-1)+1
=2n^2-4n+2+3n-3+1
=2n^2+3n+1 - 4n-1
Sn-S(n-1)=2n^2+3n+1-2n^2-3n-1+4n+1
an=4n+1 (n＞1)
a1=s1=6,