Question

已知Sn=3n²+2n,求数列的通项an

Answer 1

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