a11an13Snn的精选

问题详情：数列{an}的前n项和为Sn,若a1=1,an+1=3Sn(n≥1),则a6=()A.3×44B.3×44+1C.44                       D.44+1【回答】A.因为an+1=3Sn,所以an=3Sn-1(n≥2),两式相减得:an+1-an=3an,即=4...