数列an的前n项和Sn=n²+2n(N∈N+,n≥1),则数列通项an

数列an的前n项和Sn=n²+2n(N∈N+,n≥1),则数列通项an
数列an的前n项和Sn=n²+2n(N∈N+,n≥1),则数列通项an

数列an的前n项和Sn=n²+2n(N∈N+,n≥1),则数列通项an
∵Sn=n²+2n
∴a(n+1)=s(n+1)-sn
=2n+3
=2(n+1)+1
∴an=2n+1