Question

已知数列an的前n项和sn方=3n方-2n+1,求an的通项公式

Answer 1

∵Sn=3n²-2n+1

∴a1=S1=3×1²-2×1+1=2

S(n-1)=3(n-1)²-2(n-1)+1

=3(n²-2n+1)-2n+2+1

=3n²-8n+6

an=Sn-S(n-1)

=6n-5

∴an=2 (n=1)

an=6n-5 (n>1)