已知Sn=3n²+2n,求数列的通项an

已知Sn=3n²+2n,求数列的通项an
已知Sn=3n²+2n,求数列的通项an

已知Sn=3n²+2n,求数列的通项an
Sn=3n^2+2n
S(n-1)=3(n-1)^2+2(n-1)
故an=Sn-S(n-1)=3[n^2-(n-1)^2]+2
=3(2n-1)+2
=6n-1 (n>=2)
当n=1时,S1=a1=5
故数列的通项为
an=6n-1