a11an13Snn的精選

問題詳情：數列{an}的前n項和為Sn,若a1=1,an+1=3Sn(n≥1),則a6=()A.3×44B.3×44+1C.44                       D.44+1【回答】A.因為an+1=3Sn,所以an=3Sn-1(n≥2),兩式相減得:an+1-an=3an,即=4...