Sn3an2n的精选

问题详情：记数列的前n项和为Sn,若Sn=3an+2n-3,则数列的通项公式为an=.【回答】2-解析当n=1时,S1=a1=3a1-1,解得a1=;当n≥2时,Sn=3an+2n-3,Sn-1=3an-1+2n-5,两式相减可得an=3an-3an-1+2,故an=an-1-1.设an+λ=(an-1+λ),...